One Piece Chapter 1056, "Cross Guild," introduced audiences to a powerful new force in the pirate world-- Cross Guild. Not only is it putting out bounties on the Marines and effectively turning the tables on them, but its biggest members include Buggy, Dracule Mihawk, and Crocodile. Buggy is obviously a weak link in terms of power, but there's a debate to be had as to whether the same can be said for Crocodile.
It's difficult to gauge just how powerful Crocodile is. On the one hand, he's one of the earliest major villains of the series; in most shonen battle series, that would mean that everyone else has become exponentially stronger than him. On the other hand, Eiichiro Oda clearly has more for him to do before the story ends. Perhaps the former Warlord really does have a way to make a name for himself among all of the powerful forces in the New World. If he does, then he may still be a danger that Monkey D Luffy and the rest of the Straw Hat Pirates will have to watch out for.
However, that loss all the way back in Alabasta can't simply be overlooked. Despite being heralded as one of the Seven Warlords at the time, Luffy was somehow strong enough to beat him in a fight. Either Luffy was much tougher than everyone thought he was, or the point of entry for Warlords wasn't actually that high.
Crocodile's true potential was shown at the War of the Best at Marineford. Here, he managed to hold his own against the likes of Doflamingo, Mihawk, and even Admiral Akainu. He also tried to take Whitebeard's head, though even if Luffy hadn't stopped him, that probably wouldn't have gone as well as he'd imagined. Regardless, given how powerful his opponents have proven to be in their own rights, Crocodile handling them in any capacity should speak to how powerful he is.
Fans have been scratching their heads for the longest time about what changed between Alabasta and Marineford. Some like to attribute Luffy's win to plot armor. This would mean that Crocodile has always been strong, but Luffy beat him because that was the only way for the story to progress.
The more likely explanation, however, is that Crocodile simply got stronger between Alabasta and Marineford. As is traditional with shonen battle anime, he might have been improving offscreen so that he'd be strong enough for his big comeback. However it happened, it's safe to assume that Crocodile going forward will be as formidable as the story needs him to be.
Further proof of Crocodile's strength can arguably be found in One Piece: Stampede. In this movie, he's seen supporting the likes of Trafalgar Law, Sabo, Luffy, Boa Hancock, Rob Lucci, and Smoker in the final battle against Douglas Bullet. Even if he's presumed to be the weakest of this group, to enter this final battle and have an impact on par with the others would require him to be fairly strong; it's a high bar of entry that even members of the Worst Generation couldn't get over. As an aside, this fight can arguably be taken to imply that Lucci, Hancock, and Smoker are also all stronger than they were in their last canon appearance.
This same movie also sees Crocodile clash with Roronoa Zoro. It's very brief, but the fact that Zoro was required to suppress him should show how powerful the two of them have gotten in the last two years. If anything in this movie can be translated into the manga canon, it should mean that he's not at Luffy's level, but he's still strong enough to go up against any other Straw Hats.
For where the canon story seems to be going, Crocodile still being a threat to Luffy's crewmates seems like a reasonable assumption. The Cross Guild poster implies that Crocodile and Mihawk are subservient to Buggy. If the Straw Hats were ever to come to blows with this alliance, one of them might be left to deal with Crocodile while Luffy dealt with the boss. As for how Buggy can be a credible threat or how he even got to be the leader in the first place, that's a discussion for another time.
Narratively speaking, if Crocodile were to fight another Straw Hat again, making it somebody besides Luffy or Zoro would make the most sense. Having Luffy go up against him as some sort of central antagonist again would be repetitive and wouldn't prove anything about his strength the audience doesn't already firmly believe. Zoro would probably end up fighting Mihawk since the two of them were supposed to fight again anyway. Having Crocodile go up against one of the crewmates who knew him from Alabasta would be an ideal way to show just how far they've come in their own right. Of course, since he's apparently being presented as one of Cross Guild's strongest members, he may simply go to Sanji.
Of course, there's still a way for Crocodile to be a massive threat in his own right-- the Ancient Weapon, Pluton. He's one of the few important characters in One Piece who's been actively searching for the "World's Worst Battleship." Additionally, Caribou recently discovered that Pluton is in Wano and is eager to tell a "certain someone;" this could mean anybody, but Crocodile seems like the most likely candidate, especially since his Cross Guild poster was revealed later in the same chapter. If Crocodile were to gain control of this island-destroying power, he'd become a threat not just to the Straw Hats but to the whole world.
As things stand, Crocodile is certainly somebody to look out for. Currently, he's probably not strong enough to give Luffy a challenge, nor should he be. However, he should be just the right level of difficulty for any other member. Obtaining Pluton could also make him both a credible threat and a major character in One Piece's overarching story again. He may only be a commanding officer in Cross Guild, but he's also got plenty of pride and ambition to strive for bigger and better things.