Well the best of the advocates of the ultimate purity of the spirit make it to the highest formless realm while the annihilations ”only” make it to the lowest formless realm so you can’t really say that the lowest is the best just because it is says ”the best” conviction. A conviction is just that, one is only convinced that it is true or proper.
”There are some ascetics and brahmins who advocate the ultimate purity of the spirit. This is the best of the advocates of the ultimate purity of the spirit, that is, when someone, going totally beyond the dimension of nothingness, enters and remains in the dimension of neither perception nor non-perception. They teach Dhamma in order to directly know and realize this. Some sentient beings have such a doctrine. But even the sentient beings who have such a doctrine decay and perish.”
Yes various ascetics claim to have their own ultimate extinguishment as you can see in the sutta. The dimension of nothingness is ultimate extinguishment compared to rupa loka and kama loka, they are repulsed by continued existence and not repulsed by the cessation of continued existence in kama loka and rupa loka and in that context they have truly reached ”ultimate extinguishment”.
Likewise the best of the advocates of the ultimate purity of the spirit make it to the dimension of neither perception nor non-perception which should be seen as an even greater ultimate extinguishment than the annihilations.
The Buddha differs in advocating complete extinguishment, beyond samsara and all activities.
How could the Buddha know that the formless realms are impermanent? If Nibbāna equals being 100% unconscious, it is impossible to gain any such insights.
From the The Aṭṭha Vimokkhe (Eight Liberations) According to Sarvāstivāda:
The seventh liberation is transcending all aspects of neither perception nor non-perception and abiding in a state beyond thought and non-thought.
The eighth liberation is transcending all aspects of thought and non-thought, illuminating all worlds equally, and remaining motionless.
This on the other hand makes perfect sense:
illuminating all worlds equally, and remaining motionless = Consciousness where nothing appears, infinite, luminous all-round.
(Now the annihilationists will try to point out that ”Consciousness where nothing appears, infinite, luminous all-round” is arupa loka, but please don’t bother making the false claim - it is not. To read about arupa loka and forming a concept and actually experiencing arupa loka are two very different things).
This idea and concept that one is annihilated as in being unconscious is just a concept and not a reality. Yamaka realised that he couldn’t pin down the Tathāgata.
“In that case, Reverend Yamaka, since you don’t actually find the Realized One in the present life, is it appropriate to declare: ‘As I understand the Buddha’s teaching, a mendicant who has ended the defilements is annihilated and destroyed when their body breaks up, and doesn’t exist after death.’?”
This shows clearly that ALL the various thoughts/ideas/concepts/convictions regarding the self and also eternalism/annihilation are just that, conditional concepts and never a permanent reality - since it is all within samsara. The ascetics in the dimension of nothingness and the others will eventually decay and perish (probably due to all the insects…just kidding! )
Regardless where we are in Samsara we will decay and perish, but to imagine Nibbāna truly equals ”the cessation of the khandhas and nothing more” is just a concept.
So if someone meditates and thanks to this ends up in a unconscious state they have had a glimpse of complete extinguishment? Eventhough they actually fell asleep while meditating and only had dreamless sleep?
The other ascetics were never unconscious in their version of ultimate extinguishment so why imagine one is unconscious in the Buddha’s teaching?
Becoming 100% unconscious while meditating is not an incredible feat that requires deep concentration or wisdom. Quite the opposite, sloth and torpor will get you there in no time…