One Piece's essence is how wholesome you're supposed to feel when you look at Luffy being like a kid with a huge smile on his face or the Pirate King laughing at the biggest mystery of the series. This is a series about a main character who dresses like a little kid, a legend of piracy whose spirit animal is the happiest critter in Earth, a final island called Laugh Tale and a trascendental figure of a Joy Boy.
How can you even state that this series "as a Seinen with Dragon as the MC, it would be goated" even though the most fundamental parts of this, the core itself of the story, is all about heart-warming smiles, cartoonish aesthetics and a whole main plot related to joy. Dragon would fit so, so, so little with virtually everything in this series I can't help but read you as "I just don't want One Piece's fundamentals".
Just forget about this story because you aren't getting the basics, or you're getting them but you don't want them; anyways, this isn't for you. One Piece can't exist without Luffy, it's impossible, and it can't work as a seinen without wasting itself.