Yes, I am convinced that Povetkin, Haye and Wach would have Ali converting back to Christianity When you face all comers, some repeatedly in an era, that's respectable. You can't pick the one you're born in. That's kook logic.
Ali does in fact deserve the highest respect for this you are correct. He fought anywhere and he did not duck anyone (except of course a Foreman rematch but ducking a rematch is not as bad as ducking a fighter altogether). And of course it would be incredibly ridiculous of me to expect anything more from a past fighter than to beat the opponents of his own era (duh) but then again I am not the one making outrageous claims that those same past fighters would "take" Tyson, Lennox or K-bros. How many times have you seen a top 10 list with Muhammad at the top and Frazier and Foreman in top 5? Too many!

As for your quip... I think,

Povetkin UD Ali (10% punchers KO chance for Povetkin)
Haye KO6 Ali (no punchers chance for Ali)
Ali UD Wach (20% punchers chance for Wach)