I didn't know he had been scheduled to fight Moorer in 1992. Id have to favor Mercer in that fight because of the durability factor.
I don't know. Tillis was completely shot when he fought Morrison. Id say Witherspoon who starched Tillis in one when Tillis could still fight and Tyson probably hit harder than Morrison. In any event they were much better all around fighters than Morrison.
I think Wlad was an overall better puncher, but I have to give Lewis the edge on the right hand. I personally don't think his right, when landed flush and full force, was terribly far away in power compared to Wilder. That said, it's hard to tell.
What's strange is that Mercer claimed that Lewis hit harder than Wlad just after he fought the latter (see 36:40 in the link below). This content is protected He also said in a documentary about Tommy Morrison that he was the hardest puncher he ever faced.
We can alternate all three of them power wise and have his statements make sense, Shannon Briggs does the same when talking about Foreman, Lewis, and Vitali.
Him changing his answer between the three fighters makes sense, as often when you get to the upper echelon of power in boxing, you may not be able to put down a solid answer for who the strongest puncher you faced may be. Happens all the time.