It's very difficult to have great combat AI in an open world game, according to my video game developer relative.

There are just too many complexities involved, where even minor improvements in some aspects of AI behavior can often cause the game to break.

It's not impossible though, I've played mods going as far back as the original S.T.A.L.K.E.R. that managed to tweak the AI to where it was on par with the likes of F.E.A.R.

I don't know its its possible to achieve that level of balance and refinement in an open world game right out of the gate however.