It’s not about being identical, it’s about them having the same dynamic to Luffy.
Garp and Roger’s dynamic is completely different from Luffys and Coby’s, Coby is an entirely different thing. Hell his literal dream is the one thing Garp refuses to do, become an admiral. Coby is a different thing from Garp entirely, Coby is what the world thought Garp was, a hero. He’ll do what heroes do and save people. That’s his role, and the hero saving the slaves from the corrupt king is a tale as old as time. Coby vs Pizarro is going to happen and it’s nothing to do with power scaling, but everything to do with Coby and his role and character.
There’s a monstrous gap between Lafitte and Brook… Lafitte is literally the only BBP that Ace didn’t instantly wreck in Banaro Island. Lafitte threatened to kill Pizarro when Pizarro said he’d take over as captain, and Lafitte was serious with it. He got hyped up by an old legend in Tsuru. He is given a role that’s only shared by the number 2 of the revs, an old legend who fought Whitebeard and Garp, and a character who fought his crews vice captain to a draw. Lafitte is a top member of the BBP. Comparing him to Brook is a wild statement.