Villains come and go but One Piece has done something to keep their enemies fresh in our minds and it can be summed up in two words: power crawl.
What is that you ask? A power crawl is how a show (anime) progresses in powerful acts, characters, and struggles. DBZ is probably the most famous example.
Not too long after DBZ took off there were characters who could literally destroy planets with their finger tips. Later power levels stopped mattering altogehter because there was no physical way to gauge their detructive powers. People could never tell how even or unfair a fight was until the music really settled in.
One piece got it right. It has consistently, and evenly, brought newer and more powerful villains while keeping our heroes at an even pace. But the villains are the most important point. They have created believable barriers for the heroes to overcome and allowed us to see the progression of power–not simply the result.
Because there are so many enemies in the One Piece world I will only use a few here as examples. Blackbeard is perhaps the most notable villain in One Piece. He and Luffy are after the same goal but Blackbeard is the antithesis of Luffy. He is his polar opposite in almost every way. There was even an episode dedicated to this many (many) years ago. Most fans are well aware that Blackbeard will be the final (or at last second to last) main villain that Luffy encounters because Luffy will essentally be conquering the dark side of himself.
Rob Lucci is one of the more notable enemies in One Piece. It was one first times that we actually saw Luffy go hand-to-hand with a more skillful fighter, though Luffy was stronger. It reminded many of Goku fighting Frieza for the first time which shouldn’t be a surprise.
One Piece has been spoken of as the spiritual successor of Dragonball Z and it’s no surprise that a character like Rob Lucci adopts some qualities similar to Frieza. Both are cold, calculating, master strategic fighters that are both thwarted. In recent years Frieza has made a comeback similar to Rob Lucci. But with Rob Lucci he appears to fighting with new purpose giving the character a hidden depth until later.
Katakuri brought shock to One Piece fans because Katakuri was essentially a larger more advanced version of Luffy. Fans got to see Luffy actually struggle in battle, and still come up short, against his more powerful self.
What Oda, the creator of One Piece, has done is now bring up the power levels of villains to the point where it seems that the series will follow for the next years. With Luffy battling Yonko that have been shown to push him aside like a house hold fly the entire series seems to focus on how Luffy will get stronger and it doesn’t seem like it’s going to be another two year break for the Straw hat crew.
Fans will enjoy the One Piece structure as they get to see Luffy and others become stronger in real time. Simply put the Yonko are too powerful. There won’t be a simple powering up anymore. That won’t work. Luffy’s gear 4th technique has been shown to be basically useless. At this point in the show we will likel, and finally, get to see the true nature of the devil fruits come and show us how power really works behind the seen.