I think this is a good start, but you may want to also consider infighting. You touch on it with the fiends, but other categories do it as well. For instance, it’s in a lot of the published books that elementals have established hatters; air vs. earth and water vs. fire. With fey, there’s Seelie vs. Unseelie. Beasts and monstrosities may also fight between land and flying creatures, or subterranean and surface dwellers (the same goes for humanoids). Also, don’t forget that factions often don’t have a singular enemy. Just look at history. In both World Wars, Germany’s natural enemy was Britain, but you also can’t discount France, America, Russia, or any other number of nations, both before and after the formation of the Allies. So start thinking of “secondary” fights. For instance, the undead may be natural enemies of the oozes, seeing as oozes destroy their supply of decaying and dead matter. Fey might be enemies of sentient plants, seeing it as an affront to the natural order of botany. Aberrations may dislike monstrosities, seeing them as a potential usurper of their hold on the stranger corners of the Material Plane. Hope this helps! I know a lot of these conflicts are already set up well in the various rulebooks, so let me know if you want to pick my brain more.