In a fight the opponent would very likely feel out your concealed gun, you would not fear them stealing the weapon during the fight and using it against you?
I've been in around 30 fights in my life when I was younger, I know how the psychology works, as soon as the moment both people have thrown punches the fight WILL escalate. Drawing a weapon has nothing to do with that. So they draw a knife, and you draw your gun, so what? They could still stab you multiple times after you shoot them. People are not going to just drop dead instantly after a few bullets. Even a typical bullet to the heart, they'll still have at least 5 seconds to stab you, which is plenty of time to do similar damage back to you. Only way to instantly take them down is a shot to the head, but the bullet often does not penetrate the skull.
I digress, my point is that if you're throwing punches in a fight, and it hasn't escalated to a life/death situation, then why the hell would you be in the fight in the first place? For fun? That first punch you throw back to your attacker WILL escalate the fight, your life will be in jeopardy, that's how fights work. We're not boys anymore when we can just play fight.