Maybe I'm trippin, didn't Povetkin have a belt? I think given how "in" the mix they were I'd say Cleveland Williams or Tua. Tua has 5 wins over former or future champs and never getting a belt.
Looking back now, Id throw in Tommy Morrison. The WBO was looked at as a minor title belts in the late 80's early 90s and didn't really get recognized as a Major title until 2004. So in all reality that's the same thing as someone being the IBO champion today.
Baby Joe Messi for me, somewhat limited but always in fun fights, wish his career wasn’t taken from him and that we could have seen him fight more.
I'll go with Shavers. Fought in the greatest era, had two tough fights with Holmes including sitting Larry down a couple of times, a tough fight with Ali, wins over Ellis, Norton, Bugner and Young. In any other era he probably wins a belt and defends it a few times too.
When I think about this question, honestly, I treat the so-called coloured heavyweight title as being as valid as the regarded-as-major ABC titles now. Which is EXACTLY how I view Dempsey's title, for instance, or Jeffries', despite it being lineal. Because guys like Langford won the highest title they were allowed, and I don't think it's worth any less than the title of the guys who wouldn't or just didn't fight them, when a meritocracy would dictate they so do. So, to me, this kind of thing will fall on someone like Ruddock, Tua, Ibeabuchi, Quarry. Guys like that, where it seems like sort of dumb luck that nothing fell into their hands for at least a fight. If you don't count this perverse "regular champion" nonsense with Povetkin, I do fully agree he's in that conversation. If you count coloured HW titlists, of course we're going to talk about Langford and I have to say, I wonder what would've happened to the Archie Moore who fought Marciano, if he'd mixed it with guys like Langford, McVey, Jeannette, Wills, etc. That'd be...interesting. I tend to think Ibeabuchi would've just tanked through a large swath of guys who make up the records of the star heavies who challenged for their titles. It's hard to pick one though, seeing as how there are going to be so many hairs being split and the peculiar circumstances of racial divisions from the early era.
He had a WBA "regular" title. Don't count to me. I would count the "negro" belt of Langford and Wills before I would count that nonsense.
Watching Tyson-Ruddock II right now and man he was good. He'd be a world champion in today's era of heavyweights no doubt.