The AI is good, but the enemies are only allowed to work within the confines of specific areas, so once those areas are learned, it's easy to exploit. I guess it's not necessarily that the "AI is bad", it's that the "enemy location encounter design" is bad where it gives you a small area to engage enemies in and they won't let enemies really deviate too far from that area because it's all instanced for only you within the confines of the overall spawned game world that is supposed to feel like you're playing with others.
AI is great within a small confined area, then it becomes broken as it reaches the boundaries of their allowed engagement area.