I've seen a lot of people claiming that either Crocodile got stronger in prison (like wtf, he was literally in chains), or that Oda retconned his power in Marineford to be stronger than Alabasta. Both of those are false. The first reason is that Luffy could still beat the crap out of Crocodile if he wanted to. If Crocodile got that much stronger, he would easily dispose of Luffy. He couldn't. The second reason is that Crocodile's status was in relation to other Warlords/Admirals, not Luffy. That always had to remain a constant. It is true that Crocodile was defeated when Oda thought OP would last like 5 years. But, at any point in the story, Crocodile's relation to other Warlords and Admirals had to be the same. Otherwise the whole 3 Great Powers thing wouldn't make sense. It's not like Crocodile went from 1% as strong as Mihawk to 20% overnight. He always needed to provide some sort of challenge to the other Warlords. On the other hand, Luffy's relation to the Warlords/Admirals could be changed up. Luffy was never part of a great system, so Oda could make him "weaker" in relation to the great powers. The question is, did Oda actually nerf Luffy? No. So how did he retcon Luffy's power? He made sure what Luffy excelled at -> physical strength, didn't matter as much in the grand scheme of things. So no, he didn't make Crocodile stronger, nor did he actually nerf Luffy. He expanded the range of abilities needed to become a Top Tier fighter. How did he do that? Adding Haki, Awakening, possibly FS as an addition to Haki, etc... Oda never took away anything from Crocodile. But in order to have the manga go for way more than 5 years, he simply expanded the abilities of others, and left Luffy in the dust. That way he didn't nerf anyone or retcon anything. He just made others "stronger" and Luffy remained the same, a one dimensional fighter. That was no good in the grand scheme of things.