if fighters can't be taught hand speed 'n punching power...

Physical strength and punching power are not mutual. Your boxing technique has a lot to do with KO power.

 

you can increase your punching power from the right strength and conditioning regime, technique, and balance. Plus plausibly, a trainer could teach a fighter how to generate more of their power mentally by making them throw with more intent

 

i will teach you punching power......follow these instructions carefully.......1-put a horse shoe in your boxing glove........hopefully you will score some knockouts now!

 

I know for fact since I have done it myself and helped others do it that you can :yep
Improve your balance, you have a more solid base and can transfer more energy into your punch.
Learn the right technique to pivot your foot, snap with your shoulder, turn your fist over, etc and you'll punch harder.
Then if you do drills like medicine ball throws, deadlifts, squats, plyometrics, etc, you will increase your power.

You can't turn Paulie M into Mike Tyson, but you can improve what you got

 

I've seen many folks improve punching power and speed as they progress. It's mainly just muscle memory/developing technique that does that though. And guys who are slow don't become roy jones etc. But speed and power do seem to improve a bit through practice... But the improvement is pretty limited.

 

???? Achieving the best force and velocity is a type of technique. Of course good physical conditioning is required but only to a certain point. To much muscle becomes a liability in boxing.