I think this probably oversimplifies what MN18 is saying;
“Mendicant, a person is beset by concepts of identity that emerge from the proliferation of perceptions.
“Yatonidānaṁ, bhikkhu, purisaṁ papañcasaññāsaṅkhā samudācaranti.
If they don’t find anything worth approving, welcoming, or getting attached to in the source from which these arise,
Ettha ce natthi abhinanditabbaṁ abhivaditabbaṁ ajjhositabbaṁ.
just this is the end of the underlying tendencies to desire, repulsion, views, doubt, conceit, the desire to be reborn, and ignorance. This is the end of taking up the rod and the sword, the end of quarrels, arguments, and disputes, of accusations, divisive speech, and lies.
Esevanto rāgānusayānaṁ, esevanto paṭighānusayānaṁ, esevanto diṭṭhānusayānaṁ, esevanto vicikicchānusayānaṁ, esevanto mānānusayānaṁ, esevanto bhavarāgānusayānaṁ, esevanto avijjānusayānaṁ, esevanto daṇḍādānasatthādānakalahaviggahavivādatuvaṁtuvaṁpesuññamusāvādānaṁ.
This is where these bad, unskillful qualities cease without anything left over.”
Etthete pāpakā akusalā dhammā aparisesā nirujjhantī”ti.
That is what the Buddha said.
Idamavoca bhagavā.
So in the original statement by the Buddha, it’s the not finding “anything worth approving, welcoming, or getting attached to in the source from which these (proliferations) arise” that is “where these bad, unskillful qualities cease without anything left over” (i.e nibanna).
Mahākaccāna’s analysis can make it sound like the cessation of proliferation itself is nibanna, but a moments reflection tells us that this cannot be correct, as then the second jhana, where vitakka ceases, would be nibanna, as proliferation depends on vitakka, as per Mahākaccāna:
Eye consciousness arises dependent on the eye and sights. The meeting of the three is contact. Contact is a condition for feeling. What you feel, you perceive. What you perceive, you think about. What you think about, you proliferate. What you proliferate about is the source from which a person is beset by concepts of identity that emerge from the proliferation of perceptions. This occurs with respect to sights known by the eye in the past, future, and present.
Cakkhuñcāvuso, paṭicca rūpe ca uppajjati cakkhuviññāṇaṁ, tiṇṇaṁ saṅgati phasso, phassapaccayā vedanā, yaṁ vedeti taṁ sañjānāti, yaṁ sañjānāti taṁ vitakketi, yaṁ vitakketi taṁ papañceti, yaṁ papañceti tatonidānaṁ purisaṁ papañcasaññāsaṅkhā samudācaranti atītānāgatapaccuppannesu cakkhuviññeyyesu rūpesu.
When there is what’s known as thought, it’s possible to point out what’s known as ‘being beset by concepts of identity that emerge from the proliferation of perceptions’.
Vitakkapaññattiyā sati papañcasaññāsaṅkhāsamudācaraṇapaññattiṁ paññāpessatīti—ṭhānametaṁ vijjati.
So what the Buddha is saying is that the source of proliferation is our attachment to sense contacts, and achieving non-attachment means proliferation will naturally cease, the Mahākaccāna analysis makes proliferation the “source” of what is due to proliferation, but this is simply a way of wedging the contact dependence formula into the sutta, and should not be taken literally (as this would make it nonsensical, and give rise to the second jhana as enlightenment issue).
for further reference, here is basically every word in the 4 principle Nikayas about the issue:
For he is able to recollect the caste, names, clans, life-span, chief disciples, and gatherings of disciples of the Buddhas of the past who have become completely extinguished, cut off proliferation, cut off the track, finished off the cycle, and transcended suffering.
Yatra hi nāma tathāgato atīte buddhe parinibbute chinnapapañce chinnavaṭume pariyādinnavaṭṭe sabbadukkhavītivatte jātitopi anussarissati, nāmatopi anussarissati, gottatopi anussarissati, āyuppamāṇatopi anussarissati, sāvakayugatopi anussarissati, sāvakasannipātatopi anussarissati:
DN14 and MN123 and SN35.83
“But what is the source of thought?”
“Vitakko pana, mārisa, kiṁnidāno kiṁsamudayo kiṁjātiko kiṁpabhavo; kismiṁ sati vitakko hoti; kismiṁ asati vitakko na hotī”ti?
“Concepts of identity that emerge from the proliferation of perceptions are the source of thoughts.”
“Vitakko kho, devānaminda, papañcasaññāsaṅkhānidāno papañcasaññāsaṅkhāsamudayo papañcasaññāsaṅkhājātiko papañcasaññāsaṅkhāpabhavo; papañcasaññāsaṅkhāya sati vitakko hoti; papañcasaññāsaṅkhāya asati vitakko na hotī”ti.
DN21
‘But is that goal for those who enjoy proliferation or for those who enjoy non-proliferation?’
‘Sā panāvuso, niṭṭhā papañcārāmassa papañcaratino udāhu nippapañcārāmassa nippapañcaratino’ti?
Answering rightly, the wanderers would say:
Sammā byākaramānā, bhikkhave, aññatitthiyā paribbājakā evaṁ byākareyyuṁ:
‘It’s for those who enjoy non-proliferation, not for those who enjoy proliferation.’
‘nippapañcārāmassāvuso, sā niṭṭhā nippapañcaratino, na sā niṭṭhā papañcārāmassa papañcaratino’ti.
MN11
“Mendicant, a person is beset by concepts of identity that emerge from the proliferation of perceptions.
“Yatonidānaṁ, bhikkhu, purisaṁ papañcasaññāsaṅkhā samudācaranti.
If they don’t find anything worth approving, welcoming, or getting attached to in the source from which these arise,
Ettha ce natthi abhinanditabbaṁ abhivaditabbaṁ ajjhositabbaṁ.
just this is the end of the underlying tendencies to desire, repulsion, views, doubt, conceit, the desire to be reborn, and ignorance. This is the end of taking up the rod and the sword, the end of quarrels, arguments, and disputes, of accusations, divisive speech, and lies.
Esevanto rāgānusayānaṁ, esevanto paṭighānusayānaṁ, esevanto diṭṭhānusayānaṁ, esevanto vicikicchānusayānaṁ, esevanto mānānusayānaṁ, esevanto bhavarāgānusayānaṁ, esevanto avijjānusayānaṁ, esevanto daṇḍādānasatthādānakalahaviggahavivādatuvaṁtuvaṁpesuññamusāvādānaṁ.
This is where these bad, unskillful qualities cease without anything left over.”
Etthete pāpakā akusalā dhammā aparisesā nirujjhantī”ti.
That is what the Buddha said.
Idamavoca bhagavā.
Eye consciousness arises dependent on the eye and sights. The meeting of the three is contact. Contact is a condition for feeling. What you feel, you perceive. What you perceive, you think about. What you think about, you proliferate. What you proliferate about is the source from which a person is beset by concepts of identity that emerge from the proliferation of perceptions. This occurs with respect to sights known by the eye in the past, future, and present.
Cakkhuñcāvuso, paṭicca rūpe ca uppajjati cakkhuviññāṇaṁ, tiṇṇaṁ saṅgati phasso, phassapaccayā vedanā, yaṁ vedeti taṁ sañjānāti, yaṁ sañjānāti taṁ vitakketi, yaṁ vitakketi taṁ papañceti, yaṁ papañceti tatonidānaṁ purisaṁ papañcasaññāsaṅkhā samudācaranti atītānāgatapaccuppannesu cakkhuviññeyyesu rūpesu.
When there is what’s known as thought, it’s possible to point out what’s known as ‘being beset by concepts of identity that emerge from the proliferation of perceptions’.
Vitakkapaññattiyā sati papañcasaññāsaṅkhāsamudācaraṇapaññattiṁ paññāpessatīti—ṭhānametaṁ vijjati.
MN18
he’s tamed, and doesn’t proliferate:
Dantassa nippapañcassa,
MN56
People generally let their perceptions proliferate;
Papañcasaññā itarītarā narā,
perceiving and proliferating, they are attracted.
Papañcayantā upayanti saññino;
When you’ve expelled all thoughts of the lay life,
Manomayaṁ gehasitañca sabbaṁ,
wander intent on renunciation.
Panujja nekkhammasitaṁ irīyati.
SN35.94
These are all proliferations: ‘I am’, ‘I am this’, ‘I will be’, ‘I will not be’, ‘I will have form’, ‘I will be formless’, ‘I will be percipient’, ‘I will be non-percipient’, ‘I will be neither percipient nor non-percipient.’
‘Asmī’ti, bhikkhave, papañcitametaṁ, ‘ayamahamasmī’ti papañcitametaṁ, ‘bhavissan’ti …pe… ‘na bhavissan’ti … ‘rūpī bhavissan’ti … ‘arūpī bhavissan’ti … ‘saññī bhavissan’ti … ‘asaññī bhavissan’ti … ‘nevasaññīnāsaññī bhavissan’ti papañcitametaṁ.
Proliferation is a disease, a boil, a dart.
Papañcitaṁ, bhikkhave, rogo, papañcitaṁ gaṇḍo, papañcitaṁ sallaṁ.
So mendicants, you should train yourselves like this: ‘We will live with a heart free of proliferation.’
Tasmātiha, bhikkhave, ‘nippapañcena cetasā viharissāmā’ti— evañhi vo, bhikkhave, sikkhitabbaṁ.
SN35.248
“If you say that, ‘When the six fields of contact have faded away and ceased with nothing left over, something else exists’, you’re proliferating the unproliferated.
“‘Channaṁ, āvuso, phassāyatanānaṁ asesavirāganirodhā atthaññaṁ kiñcī’ti, iti vadaṁ appapañcaṁ papañceti.
If you say that ‘nothing else exists’, you’re proliferating the unproliferated.
‘Channaṁ, āvuso, phassāyatanānaṁ asesavirāganirodhā natthaññaṁ kiñcī’ti, iti vadaṁ appapañcaṁ papañceti.
If you say that ‘both something else and nothing else exist’, you’re proliferating the unproliferated.
‘Channaṁ, āvuso, phassāyatanānaṁ asesavirāganirodhā atthi ca natthi ca aññaṁ kiñcī’ti, iti vadaṁ appapañcaṁ papañceti.
If you say that ‘neither something else nor nothing else exists’, you’re proliferating the unproliferated.
‘Channaṁ, āvuso, phassāyatanānaṁ asesavirāganirodhā nevatthi no natthaññaṁ kiñcī’ti, iti vadaṁ appapañcaṁ papañceti.
The scope of proliferation extends as far as the scope of the six fields of contact.
Yāvatā, āvuso, channaṁ phassāyatanānaṁ gati tāvatā papañcassa gati;
The scope of the six fields of contact extends as far as the scope of proliferation.
yāvatā papañcassa gati tāvatā channaṁ phassāyatanānaṁ gati.
When the six fields of contact fade away and cease with nothing left over, proliferation stops and is stilled.”
Channaṁ, āvuso, phassāyatanānaṁ asesavirāganirodhā papañcanirodho papañcavūpasamo”ti.
AN4.173 and AN4.174
Take a mendicant who relishes work, talk, sleep, company, closeness, and proliferation. They love these things and like to relish them.
Idhāvuso, bhikkhu kammārāmo hoti kammarato kammārāmataṁ anuyutto, bhassārāmo hoti bhassarato bhassārāmataṁ anuyutto, niddārāmo hoti niddārato niddārāmataṁ anuyutto, saṅgaṇikārāmo hoti saṅgaṇikarato saṅgaṇikārāmataṁ anuyutto, saṁsaggārāmo hoti saṁsaggarato saṁsaggārāmataṁ anuyutto, papañcārāmo hoti papañcarato papañcārāmataṁ anuyutto.
A mendicant who lives life like this does not have a good death.
Evaṁ kho, āvuso, bhikkhu tathā tathā vihāraṁ kappeti yathā yathāssa vihāraṁ kappayato na bhaddakaṁ maraṇaṁ hoti, na bhaddikā kālakiriyā.
AN6.14
‘A Realized One exists after death’: this is just about craving. …
‘Hoti tathāgato paraṁ maraṇā’ti kho, bhikkhu, taṇhāgatametaṁ …pe…
it’s just about perception …
saññāgatametaṁ …pe…
it’s an identification …
maññitametaṁ …pe…
it’s a proliferation …
papañcitametaṁ …pe…
it’s just about grasping …
upādānagatametaṁ …pe…
‘A Realized One exists after death’: this is a regret.
‘hoti tathāgato paraṁ maraṇā’ti kho, bhikkhu, vippaṭisāro eso;
‘A Realized One doesn’t exist after death’: this is a regret.
‘na hoti tathāgato paraṁ maraṇā’ti kho, bhikkhu, vippaṭisāro eso;
‘A Realized One both exists and doesn’t exist after death’: this is a regret.
‘hoti ca na ca hoti tathāgato paraṁ maraṇā’ti kho, bhikkhu, vippaṭisāro eso;
‘A Realized One neither exists nor doesn’t exist after death’: this is a regret.
‘neva hoti na na hoti tathāgato paraṁ maraṇā’ti kho, bhikkhu, vippaṭisāro eso.
An unlearned ordinary person doesn’t understand regrets, their origin, their cessation, or the practice that leads to their cessation.
Assutavā, bhikkhu, puthujjano vippaṭisāraṁ nappajānāti, vippaṭisārasamudayaṁ nappajānāti, vippaṭisāranirodhaṁ nappajānāti, vippaṭisāranirodhagāminiṁ paṭipadaṁ nappajānāti.
AN7.54
Metta