Zoro was stronger than shown all the way up to Wano, despite not showing feats. Going by feats he was way weaker than Sanji at the end of WCI, but he obviously wasn't really.
As for BB I assume he's top tier. He's not gonna be another joke/misunderstanding yonkou (Buggy) and I don't see Oda making him fodder for narrative purposes, eg having him be weak because he's conniving and reliant on DF powers and that makes him have extremely weak haki and get one-shotted by Shanks like Kidd did. He's also always been stronger than Luffy - he could beat Ace (who was a quite strong commander) when Luffy was nowhere near, he could handle being at Marineford with only his crew for support. He's probably still around Luffy's level, which is the bottom of the top tier. He's disliked by the Whitebeard Pirates and Shanks, yet nobody has taken his territory. If he was still Ace level, Marco and co would go kick his ass.