It's different. He wasn't allowed to have the WBO and WBC at the same time. Henry Akinwande had the WBO belt and faced Lewis whilst it's champion.
The WBO wasn't considered a major world title yet when Lewis had won the Undisputed championship, the WBC has always been part of the major 3 boxing organizations, so until Usyk gets that title strap he can't be considered Undisputed even as he holds 3 out of the 4 trinkets today in the 4 belt era.
Where was Wlad when Lennox TKO'd 6 Vitali ??? When Wlad got ko'd twice Vitali jumped in & fought for his little brother . But after Lennox beat Vitali Old Wlad went AWOL !!!! ROFL Wlad knew he couldn't beat Lennox. If he'd challenged him Lennox would have fought Wlad because there was no one else worthy after TKO in 6
When Lewis beat Vitali he retired after that. I'm a Lewis fan but after Vitali he decided it was time for him to hang it up. Father time can't be beat.
Usyk is also 37 now. Same age as when Lewis retired. Should he also retired now before the Fury fight?
Here is the difference that Usyk is a small fighter compared to his opposition. It takes alot more on the body to be competitive against Super HW's. Lewis were the big guy and he could have a Wlad type of career because of his size advantage against most. Jab lean grab repeat just like he did to Mike Tyson or Wlad to Povetkin. Usyk rely on his legs.
But Lewis fought more than twice as many pro fights as Usyk has to date which will make a big difference, those extra training camps with all the extra damage taken in those fights will age you far more. Plus for Lewis motivation was a big factor in why he retired when he did. He had beaten every man other than Bowe that mattered during his era and after the Tyson fight had basically mentally checked out as he was only looking for money fights, the fact he was chasing a pointless rematch with Tyson showed he was basically going through the motions. Usyk will very likely retire for the same reasons if he beats Fury. He could continue but his motivation will likely be no longer there as he will have done everything that mattered and his legacy would have been secured and nothing he did after would really add much to it if anything at all. Wlad was rare in that he was super consistent, he was as motivated to fight a nobody like Lepai as he was a threat like Haye or Povetkin which is why he dominated for so long. Perhaps that was because he thought he still had a lot to prove as he was not appreciated as much as he should have been when champion, especially by the American fans.
For all intents and purposes Usyk already holds all the belts that aren't a joke - the WBC was a can-crushing belt at heavyweight for years and Fury hasn't exactly resanctified it with serious fights. Then again, if you're going to take that line then Joshua was in the exact position Usyk is and took a harder route getting there... But Joshua wasn't undisputed despite standing opposite an even less worthy ducker, so why would Usyk be? It's obvious who's the best, maybe this undisputed tag doesn't really matter too much.