If I recall correctly, didn't most cross-gen titles run like hot trash on X360 and PS3?
I do have a question for people here. Would you buy this game on PS4 or Xbox One if it ran at 720p-30fps (stable) ?
I wouldn't say "most" cross-gen titles last time ran that poorly, but certainly there were a few that did (like Shadow of Mordor). For the others, though it was usually clear that the PS3/360 versions weren't a major focus, performance was usually within the kind of boundaries that people would expect based on last-generation hardware - like, say, ACIV: Black Flag was a slight improvement over ACIII on PS3/360 even though it was clearly outclassed by the PS4 and Xbox One versions.
For this generation I don't think I'll bother buying anything on PS4 or Xbox One that looks like it might get anywhere near stretching those machines. I'll wait a few months and play on PS5, even if there isn't a PS5 version, since that'll still have improvements over the base PS4.
I think it rather might be CPU limitations in that game.
It might be. However, if that was the case, it'd be a little weird to single out the original Xbox One as being "extremely unsatisfactory" - if there are CPU limitations the base PS4 should have at least as many problems as the original Xbox One (and indeed more problems, considering the Xbox One's greater clock speed).