Because quick blows to the windpipe are not allowed?
Such talk is dangerous. It gives women (and sometimes small men) a false sense of security.
What happens when your quick blow misses? Normally, such a move requires the element of surprise. If he is the aggressor (if not, why are you hitting him?) you will not have surprise on your side.
I've talked to women who are confident they can easily disable a man just by using their knee to his groin. They don't realize that guarding against this move is about the first thing a man learns on the playground in elementary school.
Although your basic premise is correct. The weaker person's only hope is all-out attack aimed at disabling the other. Defensive moves are totally useless. The longer the fight lasts the greater the odds against the smaller person become.