Right off the bat, this is a terrible match for Joyce stylistically. Joyce is about jabbing and absorbing punishment. He would never get his jab going against one of the greatest jabbers the HW division has ever seen. So he's left with what, absorbing punishment? Trying to sneak in a molasses right hand? Beyond this challenge, add in the levels upon levels of difference in skill, talent, experience, etc. It's far too big an ask to even put him at 1/10 odds.
Just about every time of boxer bashed up Wladimir Klitschko. Old, short, tall, mediocre, very good, slick, power plodder, south paw, orthodox, slow footed, agile, home soil, away... Joyce definitely has a decent chance at beating him.
No, it's because they're proven elite fighters (Usyk debatable at HW, obviously not at CW) whilst Joyce has never beaten anyone who is better than a gatekeeper. If you want to talk urban myths... There's an urban myth that Joyce is a nightmare matchup for the elites even though he's never fought at anywhere near their level.
Yep, and they were wrong... But Dubois ain't all that either and may well never be... Many, many guys march up the division, create some excitement and then never get past gatekeepers (that's why we call them gatekeepers), Pricey was one and Dubois may well turn out to be another. Beating an overhyped fighter like Dubois who still has a lot of developing to do doesn't suddenly make you elite.
How many levels can there be ? It's a decent world class contender from a weak era vs an all time great from a weak era. I'd definitely say they're about 2 or 3 levels apart. It only takes 1 level apart for it to be an easy night for the better fighter and 2 levels would be a mismatch.