inFamous didn't stop PS4 version of Watchdogs.
Nothing stopped Watch_Dogs, which is a shame, haha.
It may only be a difference of a few percent - Hell, it may not be over 1% at all, but I do think Forza played a part in the sales difference. If Forza didn't exist, I'd still expect a lot more sales on PS4, but that's just the story of the generation.