To stay on topic, Kasumi is a fucking nightmare in the hands of a skilled player. She has relatively low damage specifically because it's made up by her offensive options. She can get in on you from almost any range with insane speed, can teleport back into your face off a guarded attack (that also guard breaks incidentally), can stuff nearly every character that tries to run in with 6pk or even a simple jab, and is one of the characters that can give guaranteed power blows under ceilings without needing a critical burst. Oh and let's not forget about her force tech game.
Sooo not low-tier.