Does people really compare Supernova to Luffy & Zoro?
First of all, Final Arc & Conclusion of Story & Final Power Ranking was decided since Start of One Piece which was like more than a Decade before Oda even though about Supernova, the Greatest & Strongest Duo of New Era were obviously always planned to be Luffy & Zoro, it's not like Oda gonna change his +10 Years Plan & make those Supernova stronger than Luffy/Zoro or even Equal, they are simply the Silver Medalists of New Era
Secondly, Oda himself said that "Even" after he introduced them, he expected most of them to drop off & even Law who received the most focus among most of them, Oda admitted that he didn't plan for that (Add to it the latest information that Doflamingo was gonna be part of Onigashima War instead of Dressrosa, so this explains why Oda didn't plan for Law to be that focused on before since whole Dressrosa Arc wasn't planned apparently). He said he expected only Kid to survive in New World & be relevant. That means we are not talking about +10 Years before Supernova Introduction, we are talking even after another half a Decade, Supernova weren't Planned to be that much relevant or strong to be compared to Luffy & Zoro
Thirdly, do you even know why the Dark King himself proposed to Luffy a 2 Year Training? It's so that he doesn't Fail in NW & becomes Ready & get much Stronger, something that none of other Supernova did (Except maybe Law but he still didn't Train, he was just chilling).
So the Story is clearly made so that Luffy & Zoro who spent 2 Years Preparing for NW under Two Legendary Pirates will show-up superior than other Supernova who rushed into NW without preparation
And finally, last argument is most simplest, Main Character Duo are simply Portrayed Superior than other Supernova & Oda even proved that by changing their Name to "Worst Generation" & included Teach in it who is a Yonko & shits on anyone not named Luffy or Zoro among them. So Clearly Oda is proving to you that those Supernova don't need to be comparable in Power to be comparable in being part of Worst Generation. Not to mention that both are guaranteed to become Pirate King & Strongest Swordsman, while other Supernova will achieve nothing except Extra Fame & being considered Silver Medalists
Conclusion:
Oda's Original Plan for +10 Years + Oda's Expectations even after Introducing them for +5 Years + Luffy/Zoro's Portrayal + Their 2 Year Training ... etc clearly shows that Luffy/Zoro >>>> Supernova. Put it in your head