As strategic and intelligent (albeit boring) in the ring as he was... I think the major points a lot of Non-pro Lennox contigency here is trying to make is that:
A. He didn't have the highest regarded chin. (In both of the Ko's, we was obliterated and had to be filled in later on what happened... and he was rocked by briggs and one or two others--Mavrovic maybe?.) That doesn't bode well for his chances against elite big punchers in their prime that wouldn't allow themselves to be fed the jab all day.

B. He didnt have many fights against stick and move speedsters. Most of any seek and destroy aggression deployed by Lewis came against lumbering plodders with lead feet and mental instability or green horns like michael grant who really didnt like getting hit at all.

It could also be argued that at the time he fought the older less effective versions of tyson and Holyfield, He wasn't the Lennox that average about 230lbs. He was coming in anywhere from 245-250. In fact, if he fought many of greatest heavyweights throughout history, he'd be enjoying a 20 -30 lb advantage prime for prime. So the point could also be made that Lennox looked great amongst his contemporaries because many of them were bigger, heavier and less agile...Leaving the window open for him being outboxed and outpaced by faster slicker fighters and/or being Knocked out regardless of weight due to his "less than granite" chin. Still in these fights noone knows what would happen or who would prevail...as theire are other possibilities, such as Lennox out thinking them /catching them cold/ a lucky punch/ dq's/ etc. I think the point being made though is that with many situational varibles, its possible maybe even probably that Lennox wouldn't be as dominant in any heavyweight picture you put him in.