Who has the tougher era out of these three heavyweight champs?

Louis and Holmes are close. I think I'll lead towards Louis because he left no stone unturned. But the 80's is a very underrated decade from top to bottom since there were talented belt holders who were inconsistent. Guys like Weaver, Page, Dokes, Spoon and the lot would give Louis problems at their absolute best. Very close in my opinion. But Louis edges Holmes by a smidge.

Wlad is way further south. He dominated in the worst era in heavyweight history.

 

Larry Holmes fought 43 times in the 1980s and 1990s. He fought in a combined 21 heavyweight title fights in those two decades.

Holmes fought more times in the 1980s and 1990s than Evander Holyfield AND Ray Mercer did.

Holmes engaged in more heavyweight title fights in those two decades than Holyfield (13) and Tyson (15) did.

Tyson himself only fought 49 times in the 1980s and 1990s (six times more than Holmes).

So I think those were Holmes' eras, too. He was certainly active in them.

 

Great answer.