AC's combat doesn't make AA's terrible in retrospect. AA set the stage for AC. We can acknowledge that AC's combat is as good as AA's, and the player can limit themselves to the same moves available in AA, or choose to use all the other options available to the player. There are no combat scenarios in AA that are any more tightly/deliberately designed than the ones in AC. You come across groups of guys in AA just like you do in AC. Sometimes, one guy has his back to a vent/door/window. Then you fight them all. AC is simply better than AA in that regard.
I truly believe AC's open world fundamentally changes very little about the series' structure and only allows more for the player to see/do. AA was a very guided experience with only a few parts that did something special with that linearity, things that couldn't have been accomplished in AC's (more) open world. I'd like to hear more specific examples of AA's design (really specific) since I haven't played it in a while.
They're valid for why someone would prefer one game to another, but when it comes to saying which is objectively better overall (something some people try to argue, in favor of AA), it is unconvincing. Especially when AC achieves arguably everything AA does, and then some.