Our AI hasn't interfered with anything. A lot of the AI coming from the raw Essentials v14 seems to be buggy in itself-- none of the changes I've made should have an effect on that. Presumably Maruno will correct this in future releases too. A lot of the field stuff has conflicted though, yes, because Maruno restructured the variables and some methods in the battle scripts, so a bit of our stuff had to be rewritten to fit. That's not the sort of thing that will happen every update though.
As for why we can't just take the bits we need- for something like Life Orb, sure, that would be super easy. But by contrast something like fixing the X Items- we're not really sure what part of that entire class of items was broken in the first place so we'd really just be guessing which bit of relevant code we need to copy over, and if that code happens to call to a method or variable added/changed in 14 then we might not pick up on that, or even if we do it might entail basically doing half the work that Maruno has already done for his release, over again. No bueno.
Believe me, when I was told Essentials 14 came out I was surprised, horrified, and more than ready to toss it to the side deeming it #not worth. Unfortunately the actual change list for 14 is much much longer and, regrettably, I felt it was necessary. I mean, c'mon, I don't wanna make extra work for myself either, but ultimately the quality of the resulting game is more important than how much time or work goes into it.