Alot of oldtimer would have beaten Lewis and i am going to say easily. In the fight with Tua you can see why. The big shots comed from Tua. Lewis didn't land a single clean power shot. All his punches comed from up there with no power on them and in the best case on the top of Tuas head. Lets take Marciano for example.
He is shorter. This means even fewer power shots will reach him. Second the stamina! Tua don't have it. He is unnecessery big! Third Marciano has punching power in both hands! Forth he is much more educated and i think that he woudn't go so lame inside and let Lewis tie him! This was the bigest problem from Tua. Every time he stayed outside and let Lewis commit on going away from the ropes Tua landed some insane shots!

I think that being bigger than necessery doesn't make you better fighter! Knowledge is something different!