Mech-basketball is a different game than basketball. There would be an entirely new metagame. I just watched Magnus Carlsen get checkmated in 7 moves in magic chess, a move even a 10 year old could find ( vs GM Hansen if you want so see it ).

Another analogy:

"A good archer is going to be an amazing sharpshooter and therefore I only want to field archers (with guns) as soldiers", might be a horrible way to run a modern military.

This "the best at the old thing will be the best at the new thing too!" needs to die in a fire.