I love the infighting. And if I remember ocrrectly, you can turn it off if you don't want it. But I feel the improved AI and increased spawn rate when sleeping easily makes up for the benefits of infighting.
Besides, it's led to some fantastic instances of using mobs against eachother. Just last night I managed to pacify an ancient vampire who then killed all the nemies in the room. I've also had to pull a harpy through half the dungeon to find some other mobs that could kill it since I lacked the right material
Talk about the mods or features you'd like to see in Daggerfall Unity. Give mod creators some ideas!