Implying that gif is representative of the A.I and common place is hyperbolic. Those are the shotgun rebels who charge in close range to give devastating blows and flush you out of cover, you get killed in two shots if they manage to hit you. There's a bug of some kind in that spot where if your in the cover stance, their attacks miss even though you're directly in their line of sight and wide open. I've replayed this level a bit and they don't just stand there and do nothing, here they shot at me three times but for some reason their hits don't register when I'm in cover.
Compared to when Galahad's out of cover, he gets hit by the shotgun blasts. Notice the different AI routine and one of them tries to do something else after I shoot at him.
Enemy strafing, Galahad killed in 2 hits
Different playthrough, same guy trying to get in even closer with the shotgun, different AI routine.
Enemies back up and weave in and out of cover.
Some of the other guys also try to dodge away after being shot at.
There are times where the enemies just reload their gun out in the open or slowly back up without firing at you, so the AI isn't without faults, and they're not super intelligent, but they're also not as braindead as you imply them to be. The only AI I'd call completely stupid and braindead are in those Lycan arena battles, just terrible all around there. Still would definitely like to see an improvement in AI in general if there's a sequel though.