To be honest, I'll take Lucci being crazy strong over weak and irrelevant.
He had his time as a near equal enemy to Luffy and it's nice seeing old villains grow along with the main character. My issue is the amount of focus put on Luffy getting out there and growing through battle against Warlords, Commanders and Emperors just for Lucci to be just a power-up or a few behind him somehow. Lucci can be a prodigy but Luffy's gone through so much, it seems weird just having people match him.
He obviously trained considering he's in the New World counterpart to his old CP group but strong enough to tango with G5 seems iffy. He still had a cool transformation and it's clear Luffy isn't in danger but it's nothing but wins for Luccibros.
I can't wait to see more from Crocodile. When Luffy beat him, he'd gotten all rusty and by Marineford, he was trying to get back into the right mindset and strength and even if he wasn't crazy powerful, you could see his resilience so after two years and rising to a 1.9 billion bounty, I can't wait to see him perform.
Personally, I don't think every past antagonist needs to fight Luffy specifically. With Lucci, we get the call back to One Piece's best fight and I can appreciate that but I feel like if Oda repeats ghis with every past enemy that regains relevancy, it'll get a bit tiring. Hopefully Crocodile manages to prove himself but in a new way.
I have hope for Smoker honestly. Oda just doesn't mind using a character to hype up others repeatedly. Smoker will be like Sanji, rise to the occasion when Oda feels like it.