New Vegas and Fallout 3 were borderline unplayable on PS3 when they launched too.
Old timers keep warning people not to buy on launch. But every time a 'big' game comes along, there are a lot of people who ignore the warnings and do it anyway.
Witcher 3 was the same. Roach(horse) on a roof was a meme at one point. But CDPR wasn't as famous then, so far less people played that on launch.
Oh, and while we're at it, Witcher 3 isn't a true RPG either. Cyberpunk is quite a lot like Witcher 3 IMHO.