One advantage of One Piece's lengthy storytelling is being allowed to revisit certain characters, whether they're villains, authority figures, or notable bystanders to the action. It makes it feel like a living world rather than a simple pattern of increasingly powerful obstacles for Luffy to topple, and the chance that a face from the past might reappear adds to the anything-can-happen allure of the series. For example, Rob Lucci showing up with the rest of his CP0 cronies in the current Egghead Island anime arc is a fun way to check in on the man who was, at one point, Luffy's most dangerous opponent - and throwing the two against one another again is perhaps the most impactful rematch that the series can offer.
When it comes to One Piece villains, what they stand for is just as important as how strong they are. Crocodile was the power-hungry leader of a secret organization, Eneru was a wannabe god who relished in keeping his "subjects" in a state of eternal paranoia, Doflamingo was a deceitful mastermind who inflicted sadistic pain as a way to control his own haunted past, and Kaido was the despotic overlord of a nation that he would just as readily starve as he would rule. Lucci was the mechanical grip of the World Government, a figure pushed past empathy and into a mindset of cold subjugation. He is a weapon to be used, terrifying for as long as the arm that uses him has enough energy to swing.
