I fail to see how it's a false equivalency.
In OP-verse, we have 3 generations so far:
- Gol D. Rogers, had multiple at the top tier level
- Newgate's, had multiple at the top tier level
- Mid gen, has multiple at the top tier level
- Luffy's, Oda is setting it up where others will catch up to Luffy eventually like Shiki/Newgate caught up to Roger.
Why would we automatically assume Joyboy compared to his own era was a God Tier person, when that has never been the case for anyone else? I'd be willing to bet anything on whoever is Garp/Dragon/Luffy's ancestor will be on par with Joyboy. He's the most important figure of that era, just like Roger was by far the most important of his era. Where as in something like Naruto for example, there's always been 1 or 2 people who were FAR above everyone else from that era, which then continues with Naruto-Sasuke.
It could simply be top tiers of Joyboy's era was simply built different, meaning Trafalgar/Portagus/etc all could have top tiers near/at joyboy's level... which wouldn't be a surprise since the Ancient Kingdom was a vastly more advanced society.
Not saying you're wrong for believing what you believe. But I don't find it likely that Joyboy's era didn't replicate the set up of any other era.