While these mods do have some inherent compatibility issues it would be nice to have a way of addressing, I think 'impossible to use any two of them together' is pretty drastically overstating the issue - I use several enemy adding mods, including A Better ADVENT and several of the stand-alone ones like the ADVENT Psi Operative, and they mostly work fine with each other, to the degree of it being possible to have enemies from multiple mods in a single pod as long as they share a valid leader. The 'valid leader' is something of a sticking point, of course, but one that (short of changing the way pods as a whole are constructed) I don't think can be solved without compatibility patches. The problem is that in each new enemy's CharacterStats.ini entry, it specifically lists all enemies that are allowed to serve as followers to that enemy. Mods can append new followers to these lists (and multiple mods can add to the same ones, which is why the mods sort of work with each other already), but for a mod-added leader enemy to accept a mod-added follower from a different mod, that follower would needed to be added to the leader's whitelist, and I don't know how, if at all, that would be done automatically, at least not in a way that was intelligent, so as to not, say, give one of A Better ADVENT's new Captain variants the Muton Demolisher as a follower, when vanilla Captains can only lead ADVENT units.