its a bit of a daft question in someways because a boxxers physical advantages are his weopons

mayweather wouldnt be as good if he wasnt so quick
lewis wouldnt have been so good if he wasnt so big

but lewis would have fought a different style if he was a few inches shorter and more than likely would still have been a success

wlad klit tho relies so heavily on his size, he protects his chin with his size

I would say take away klits size he wouldnt be anywhere near world champ