A reversal doesn't have to be 1 frame to be useful. It just has to have invulnerability. Unless your Tager, in which case it doesn't matter what you do because your character sucks.
SIR is a terrible "reversal" though, I must admit. I've been 720'd out of it so many times. Or just lost the game because it has like practically 0 (actually 0?) invulnerability frames so you always trade instead of countering.
Probably the #1 move that's invulnerable that you should never use as a reversal is Led Ley >_>