I wouldn't say that, I have AC4, WD and Splinter Cell Blacklist all on the PC and they all play fine and without any issues. Now if the problem people have is with online and multiplayer stuff, then I guess I'm lucky since I only play these games for the single player.
Im on NVIDIA for my GPU now, but back when I had an AMD card, I would get roughly half the FPS of the equivalent NVIDIA card, UPlay would constantly lose connection to the servers then kick me out the game, every time a popular game comes out, half the time the servers die completely and PC players can't even play it, sometimes for days. Even on an NVIDIA card their games are unoptimised garbage for PC.
Ubisoft have shown nothing but contempt for the PC market.