Here are some reasons on why I believe Eustass Kid is a big deal, based off the narrative of the story given so far.

When the Supernovas were first mentioned, Oda had heavily hinted and emphasized Kid to be one of Luffy’s main rivals in the story, by giving Kid a slightly higher bounty than Luffy. Therefore isolating him and making him standout from the rest of the Supernovas.

Eustass Kid is the only supernova other than Luffy and more so than Law, that Oda has been setting up to claim a victory against a Yonko.

Luffy and Kid are the only supernovas that have a strong parallel with each other, in the sense that they both have challenged multiple Yonkos along their journey to become the pirate king.

I believe the trio rivalry of Luffy, Kid, and Law, is a intertwined fate that is shared with each other, but mainly because of the “Will of D.”, which Kid is apart of.

Luffy is unaware of his “D” name and Law is a bit more aware of the name, yet has no specific knowledge. I believe Kid is unknowing of his hidden “D” name, as we’ve seen strange circumstances occur in the birth of characters in the story.

Regardless of Kid’s wicked nature, I believe you can still be a “D”, because Oda has shown characters with such behaviours.

Of all the supernova captains Oda decided to station at the slave auction house, it happen to be Luffy, Kid, and Law, and I believe it was the fate of “The People of D” that had brought them there.

I think the future battle between the people of “D” and the celestial dragons will consist of Luffy, Kid, and Law, as part of the main fighters.

I believe these three individuals who carry the “D” will achieve great victories against the “Gods” that will forever change the one piece world.

Based off Kid’s ruthless nature and cynical view of the world, he must have had a harsh childhood growing up. Oda has been slowly but surely setting up Kid’s tragic backstory.

I believe after Wano the pirate that will be a prominent figure in the one piece world and who rivals Luffy along with Blackbeard, is Eustass “Captain” Kid.