I find the stock AI still have many issues which make them less than believable.
1) They don't reload! (darn Hollywood armament).
2) They react instantly.
3) They shoot before they have even turned to face the player ..
4) … and worse the player gets hit!
5) They sometimes still climb vertical faces in the terrain.
But they are taking cover way better now so that's a plus.
(I'm not really a fan of that silly Hollywood rolling around they do though!)
As ex-forces myself they just look rather comical tbh.
Been there, done that, got all the T-Shirts!