Cait's ultimate

Hello,ik how u feel when you are playing Cait and u see a enemy with really low hp in backing mode and ur like lets ult them but ur ult windup is too long for u to shoot,so why Cait's ult doesnt have a fast use i mean instead of wating the full duration u can instead use it mid-windup but u get a chance to MISS.Like a fast shot ? Sorry for the bad english its not my main language.