Hi @silence ! you may be interested in some patterns I have come across in looking for ways to provoke @sujato in relation to his Gist theory 
the Nikayas are approximately
DN: 173,906
MN: 294,643
SN: 357,384
AN: 388,889
words long.
comparing the Nikayas for doctrinal terms in the Digital Pali Dictionary’s frequency tool gives:
arahant vs ariya:
arahant
DN: 367
MN: 336
SN: 255
AN: 340
ariya
DN: 109
MN: 282
SN: 589
AN: 265
So as a taster we have DN mentioning arahant more than 3 times as frequently as it mentions ariya, and mentioning arahant more often than the almost twice as long SN, while SN mentions ariya twice as often as it does arahant, mentioning ariya almost six times as often as the half as long DN.
In fact SN is the only Nikaya to mention arahants less than 300 times.
SN mentions ariya well over 200 times more often than the similarly long AN.
SN is the only Nikaya to mention ariya more often than arahant.
kamma/jhāna vs satipaṭṭhāna/upādānakkhandha/anatta:
kamma
DN: 142
MN 279
SN 73
AN 442
Here we see a stark absense of kamma from SN compared to any of the other nikayas, with it mentioning kamma half as often as the half as long DN, and one sixth as often as AN.
jhāna
DN: 119
MN: 235
SN: 180
AN: 307
Here we see SN mentioning jhāna with significantly less frequency than the other 3 Nikayas.
satipaṭṭhāna
DN: 22
MN: 34
SN: 185
AN: 45
Here we see SN mentioning satipaṭṭhāna much more frequently than the other nikayas, 4 times as much as the similarly long AN for example, and if we control for the nearly identical foundations of mindfulness suttas in MN and DN, and the 37 aides list which merely enumerates topics, then the contrast is even higher.
SN is the only Nikaya that mentions satipaṭṭhāna more often than jhāna.
upādānakkhandha
DN: 7
MN: 23
SN: 61
AN: 10
As Pande points out the occurances of upādānakkhandha in DN are all pretty palpably late, so the difference here is again even more stark than the raw numbers indicate.
anatta
DN: 17
MN: 66
SN: 215
AN: 24
Here again, SN mentions anatta almost ten times as often as the similarly long AN.
āsava vs avijjā
āsava
DN: 49
MN: 202
SN: 138
AN: 432
avijjā
DN: 4
MN: 42
SN: 157
AN: 44
Here again we see a remarkable and striking inverse, with DN mentioning āsava ten times more often than it mentions avijjā, and all the other 3 Nikayas mentioning āsava more often than avijjā, but SN the reverse, mentioning avijjā more often than āsava.
I have given just a few doctrinal terms but I am sure more examples of these kinds of distribution could be given.
I also think that dividing MN into 2 sections, perhaps into a section of the first 30 and a section of the last 120 would make the numbers even more glaring.
My impression is that as DN/MN grew, new suttas where added to MN that began to degrade in quality, like the very messy MN102 for example, and DN suttas kept getting re-written with more and more supernatural hyperbole, so a need was felt to “get back to the fundamentals” and thus SN was born, eventually providing the source for the later abbidhamma project.
Anyway, I am slowly working on an essay about it entitled “SN is different”, but thought I would share some of my bits and pieces with you as I am partly inspired by Pande and also aspire to do much more sophisticated statistical analysis of the texts one day when I learn how to use a computer properly
Metta