Casually a trained badass (or a sufficiently unhinged person) will ignore that punch and proceed to destroy you.
So unless you're a super trained boxer and can knock out everyone in one, it's a waste of time.
You lost the element of surprise and tempo.
If you want to do some damage, do it, not rely on the opponent obliging or complying.
Certainly it's better to punch them than not punch them. Many many times overwhelming violence is sufficient to win a fight. Trained people might not be as phased, true.
You lost the element of surprise and tempo. If you want to do some damage, do it, not rely on the opponent obliging or complying.