Comment Ok, even giving them the benefit of the doubt (Score 5, Informative) 262
So let's give Ubisoft the benefit of the doubt for a moment. I'm not going to slate them for the fact that you need a top-end graphics card to get good performance with all the bells and whistles. I actually quite like to see developers showing a bit of ambition when it comes to pushing the envelope on PC graphics. Let's even assume that something went badly wrong in the AMD optimisation. It's not completely unknown for things to go wrong with a GPU manufacturer at the last moment - the PC version of Rage was a hideous mess on PCs with Nvidia cards when it released, because a driver update that was anticipated between the game going golden-master and hitting the shelves turned out not to be what the developer was expecting.
But even allowing for that, how does it explain the console versions being such a mess? There are detailed performance analysis reports out there showing frankly shocking levels of performance on both of the console platforms (Playstation 4 and Xbox One - no last-gen releases for this game). Both platforms fail to hold even a consistent 30 fps, with the Playstation 4 version (which in theory should be the better of the two, as the console does have a little bit more horsepower) having some truly shocking moments where the framerate dips into the teens.
If you're used to playing games on a PC, this might not sound too shocking. After all, unless you have a particularly old PC, you can almost always salvage a playable framerate by dropping your graphics quality. But that option isn't there on a console. For action oriented games on a console, a locked 60 fps rate is the "gold standard" and is becoming almost mandatory for twitch-shooters, precision driving games and other genres that rely on rapid response times. The popularity of the Call of Duty series, generally inexplicable to PC gamers, has largely been driven by the fact that the series has long adhered to the 60 fps standard on the consoles, meaning that it has felt tighter and more precise than its competitors.
But if you can't manage a locked 60 framerate, then the general consensus is that a locked 30 framerate is an acceptable fallback. It won't feel as precise, but it at least eliminates the disconcerting impact of framerate fluctuations (particularly unpleasant when you're playing on a controller). For a console action-game to fail to manage even a locked 30 fps is pretty shocking these days. For it to be dipping into the teens suggests either misguided design choices or terrible optimisation (or both).
Plus, yeah, the whole "falling through the floor" thing is happening on consoles as well as PC. The game's broken and it's not (entirely or chiefly) down to a particular brand of graphics card.