The above does not appear to be rocket science. It appears clear from the viewpoint of realisation:
1. the earliest sermons are the core supramundane of the SN
2. the repetitions in the SN are probably later
3. the MN embellishments (such as grandiose intros, eg. MN 22, MN 38, MN 118, etc) are probably later yet rooted in the core of the SN
4. the DN is very late, with emphasis upon mythology, past Buddhas, consciousness entering mother's womb with clear-comprehension, etc. this includes similar MN suttas, such as MN 50, MN 81, MN 123, etc
5. the AN is very late or, otherwise, more likely a compilation over time, being a mixture of old & new (eg. AN 9.12; variations on jhanas & samatha-vipassana) stuff compiled in numerical format
6. there appears no evidence the Pārāyaṇa & Aṭṭhaka are old just because they use older poetic language. these are merely teachings given in brief to non-Buddhists, which is why they are explained in detail in other texts
7. MN 135 appears late, being uncharacteristic of the Buddha's teachings about kamma
8. the SN has a few suttas out of place there (such as SN 12.51, which appears clearly illogical Abhidhamma) or one single equivalent to AN 9.12. when there are multiple suttas of a certain genre in the AN, such as the AN 9.12 genre, and merely one single equivalent in the SN, the strong impression is of a later sutta or doctrine inserted into the SN
9. of course it has been well pointed out how MN 111, MN 117, etc, contain later language (despite these suttas not being doctrinally erroneous)