The presence of a handful of references to bodhisattva practices doesn’t make the entire collection newer. It does indicate that the school that maintained it had begun to incorporate Mahayana teachings. The introduction shows that this was the case when it describes a separate bodhisattva canon being preserved at the first council.
Beyond that, EA is much smaller than AN, doesn’t engage so much in creating sutras by subdividing them into groups, and the parallels are much simpler and less expanded. E.g., the parallel to DN 2 (EA 43.7) doesn’t have the gradual path inserted into it. The parallel to the City Parable (MA 3, AN 7.67), which is EA 39.4, has a list of seven items rather than the eleven that appears in the later versions. Which makes sense as an earlier version because it’s in the Book of Sevens. It ought to only have a list of seven in its parable.
So, that’s a couple examples. There’s plenty more to discover. There’s a paper by Kuan and Bucknell (I believe) that studies the relationship between EA and AN structurally. Here is a copy of it.
The Theravada school didn’t become monolithic until later eras. Multiple schools of Buddhism coexisted in Sri Lanka for a time. Pali and Sanskrit texts existed side by side in Southeast Asia - there are inscriptions in multiple languages that show that they coexisted. I’m remembering off the top of my head at the moment, so I don’t have specific references for this, but I recall reading about it. SA does seem more likely to be Sanskritized than the other Chinese Agamas judging by its transliterations and readings.
Parallel studies actually support Theravada texts being later redactions sometimes when they agree closely with the most verbose version (which is typically the Sarvastivadin version).
I was just comparing the introductions to the Sangiti Sutra yesterday. There are two Sarvastivada versions (Sanskrit and Chinese), a Dharmaguptaka version in DA, and another Chinese version from an unknown school. The entire story about the Mallas building a meeting house is missing from DA, which has a short little setting statement that’s completely different. Meanwhile, the version in DN matches the Sarvastivada stories closely, it’s just less detailed. The version from the unknown school has a story about a single Malla layperson offering a meeting place instead of a whole group of laypeople. It’s kind of apparent that DN in that case has copied the Sarvastivada story. And also much of the dharma topics that are lists in the Sarvastivada version, too. I wrote about this a couple years ago:
The conclusion I reached is that in the case of the Sangiti Sutta, it’s a late era redaction influenced heavily by Sarvastivadins. It seems to be a compilation of multiple sources, but the Sarvastivada version was very influential. I consider the DN version the later one because it’s larger. Someone added Sarvastivada material to an older version of the sutta.
But we can’t generalize for one case like this. That’s the hard part of this: We have to go through all the parallels to get a big picture view.