Matthew was a tax collector. It would have made no sense for him to be illiterate at all. And he would have likely known Greek as it was a common language in Judea at that time.
Again, “religious writings get longer with time not shorter” doesn’t necessarily make sense either. Because the book of Jude, John’s epistles, etc were all also written later. Papyrus was expensive. It would have made sense to make an abridged work with teachings in it from your own teachers as well for difference.
Matthew has a large chiastic structure too, so I don’t know what that point was about.
Iraneus and Papias both referred to the gospels, and that was only within centuries.