Crocodile doesn't need to be a part of the worst generation, he was known well before they arrived
And why would someone like X Drake have a faster growth rate? So far Croc is a far bigger player in the story of One Piece than any supernova bar Luffy, Law and Zoro
The thing is Crocodile was weaker than Zoro(or anyone from the worse generation for the matter). Would find it personally strange if Crocodile turned out to be stronger post-skip than them considering it would mean in this case that he has faster growth rate than a youngster part of the generation of pirates the most feared, so supposed to have faster growth-rate than anyone and surpass previous generations of pirates like Law hinted when he defeated Vergo in Punk Hazard(with even pictures of Supernovas around when he said that to emphasize his words).
Oda already built up the supernovas from the worse generation to be the big players in the new world. All of them already started creating chaos in the new world according to Brownbeard and now they are forming alliance to take down yonkou, so it's not just Luffy, Law and Zoro in my opinion. They have been created for a reason
1- You know when Oda created them? Around Shabondy archipelo
2- You know why Oda created them? To create concurrence
We see here Kid, Law and Luffy trying to compete against each other:
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Here we see Law concerned about Drake:
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We see here Bonney, Capone, Hawkins, Apoo, Urouge somehow concerned by Zoro:
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Apoo says it better as well that Law shouldn't have saved a future enemy(concurrent):
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With the 2 above, the question you must ask yourself is why Oda would create rivals on the spot if the turns out to be much weaker(if at all) than Luffy during or a little after their arc introduction? Would make no sense right?
1- Law and Kid are Luffy's main rivals. True and wrong again. True because they are presented to be the rivals who will be the closest to Luffy in terms of competition somewhere around the end of the manga. Wrong because while it's true they are presented as his main rivals, it's only in the long time span. As it stands all the other supernovas are equally rivals to Luffy. Law and Kid are simply presented to be the one with the greatest potential/challenge to Luffy, not necessarly the current strongest
2- Just look at Law. 2 years prior he only had a bounty of 200millions berry, that means lower than the likes of Kid, Luffy, Drake, Hawkins. I know bounty doesn't represent strength but in my opinion it shows that Hawkins, Drake were at least around his level of strength. Infact they were the most famous according to Shakky:
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And you see how strong Law is currently right? I don't expect the likes of Kid, Drake or Hawkins to do anything less or at least be able to operate on a similar level as it stands(infact i'm pretty confident someone like Kid or Drake will end up being stronger). After all even 2years prior Hawkins, Drake, Kid and Law remained the center of attention(with Blackbeard who joined the worse generation):
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After all, Kid judged someone like Hawkins is strong enough to help him in a fight against a yonkou
3- Apoo is presented to be in conflict with Kid, even asking him to postpone their fight to when they enter the new world:
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. Not to mention he was also judged to be strong enough to be called by Kid/Killer to fight a yonkou despite Kid hating the guy:
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It shows that despite hating the guy, he was full confidence in his strength to the point he had no choice than accepting an alliance with thim
4- There is also the chapter supernovas vs 4 captains where the captains(mainly Urouge, Hawkins and Drake) were presented in similar light. Infact Urouge is the one who damaged pacifistas the most:
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5- Killer is the only non-captain besides Zoro among the worse generation. It's very likely he was created to concurrence Zoro in accomplishments. Not to mention he earlier showed to be capable to compete with Urouge with Drake intervening and telling them to settle this in the new world:
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And is now part of the alliance to face a yonkou. Infact he is the one who called Hawkins and Apoo to make the alliance(not captain Kid) as an equal
The only one i'm unsure about is Bonney and Capone considering they don't have that much hype yet but Bonney at least seemed to want to have a grudge against Luffy/Zoro because of what they did in Shabondy:
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. Not to mention she seems related to the government somehow(the way Akainu spoke to her) and judging by Capone's design, he can easily end up being a greater broker than Doflamingo