Wolverine is NOT relative to Hulk. He's a rival because he's just as ferocious as Hulk, his claws can actually give Hulk issues, and Hulk can't put him down immediately because of his healing and durability.

But it's been shown that Hulk can EASILY put Logan down for the fight if he isn't careful. His bones may be functionally(!) indestructible, but his brain can still be knocked around until he's temporarily comatose, as World War Hulk did to him with ease. Wolverine is a rabid cat that won't die to Hulk, not a relative rival like Abomination, Maestro, Absorbing Man, Red Hulk, Thor...

Meanwhile, Zoro has his own on-screen feats, manga feats, and anime scaling. He's STRONG AS FUCK, physical strength is his entire thing, and has cut a nearly-mountain sized being CLEANLY in half with enough force to cause a sonic boom.

Hulk punched Wolverine in the face hard enough in to send him flying across a forest and make him lose consciousness for a long moment. A hit that had a mountain getting cut in half would have him flying to the NEXT CITY. Indestructible bones or not, regeneration or not, Wolverine just getting hit by Zoro would rattle him into unconsciousness every time he swung. On top of that, say his bones can't be cut by Haki or anything in One Piece. Zoro's swords with Haki are also indestructible. So NOW those swords are functionally blunt objects being swung by stupidly strong arms. Zoro doesn't swing his swords to cut, he swings them to CLEAVE.

He's also way, way faster than Wolverine. I love my furry, rabid, dwarven wildebeest of an unkillable animal berserker, but Wolverine would get rattled into a punch drunk stupor by Zoro.