In Battle Mangas as One Piece there is this concept of powercreep, to sum it up briefly, every villain has to be greater then the one before, to be a threat to the ever growing protagonist. Oda knows about this and constructs his story in a way to make this concept not interfere with the story he is trying to tell.
Before I illustrate, here an example for what im about to explain and extend. Crocodile in Marineford. Crocodile in Marineford should have been comlpete fodder. Early story Luffy shafted him to a sandy prison in Impel Down where he couldn’t train his power or abilities at all, or at the very least not very much. So what did Oda do to not make Crocodile a joke in the story where the average power grew enormous since then? He simply gave Crocodile a powerup.
Oda doesn’t write frauds, he created Crocodile to be a dangerous mafia man, so Crocodile will always be dangerous, the same will apply to Enel if he returns. Oda won’t make Enel comeback and be on the same level as he was, even Nami could beat him now with Zeus. But he will give him a powerboost to still be relevant to most characters.
And now to the most current example. Mihawk. A lot of Powerscalers been doing mental gymnastics to paint Mihawk as a fraud. Mihawk is written to be the World’s Strongest Swordsman, Oda doesn’t make jokes with titles as these, Mihawk’s antifeats from Marineford mean nothing, until Mihawk is actually currently pushed no one knows how strong Mihawk is. Just like no one knew how strong Crocodile became in prison.
Mihawk will always get the power to be a ridiculous threat since Oda will have Zoro surpass the strongest swordsman and not a fraud.