Everyone and their mum knew Luffy was gonna be hype-tooled, this is exactly as expected.
The only question is whether Luffy was using ACoC in base. If he was, then Kaido looks a lil fraudulent and we can confirm Base Luffy isn't much/old Gaban is a low top-tier.
If he wasn't, then Base Luffy's feats vs Kaido remain perfectly valid since Luffy is genuinely a high-tier unless he's using either ACoC or G5. Base ACoC-less Luffy is like Queen level, of course he'd get bopped by Gaban. He'd get bopped by any YC1.