Hmm, I mean, if you're including the fight against Pucci, then yeah, Star Platinum shouldn't be that fast.
Though, you have Silver Chariot being able to react to light, and Star Platinum is about its speed.
Even so, it wouldn't be a problem for Jotaro to win if he has time stop. Star Platinum is stronger than Stone Free, whose hits are as strong as small and fast meteors, so Jotaro should be able to hurt Kenshiro.