Main Villain is most often not the Focus of Story
Literally when Luffy went to Recruit Zoro, Villain was Helmeppo, He is the one who tried to Hurt that Girl & Imprisoned Zoro & took his Swords, and He was exploiting his Position & got Luffy Angry who Punched him, and ordered that Girl who tried to feed Zoro Dead ... etc
And then boom, say Hi to Axe-Hand Morgan
Oda did this again in Baratie as well, the Drama focused on Gin, but Actual Villain was Krieg
And again in Loguetown, Buggy was the one who wanted to Kill Luffy, but it's Smoker He had to worry about
And again in Whisky Peak, when suddenly Mr. 5 Appeared
And also in Skypiea, when They first got attacked by Wyper & Luffy didn't meet Enel until the End (After War was Over)
Usopp's Arc can also be similar, as it was Jango who was attacking the Island, but it was all for Kuro
In Jaya as well, it was after Bellamy's Plot that We got Introduced to Blackbeard as the actual strongest guy visiting Jaya
Same for Long Ring Long Land, most Arc against Foxy & then say Hi to Aokiji
And again in Water 7, it was mostly an Arc about facing Franky Family, but then we got that insane CP-9 Reveal
In Thriller Bark as well, it was Hogback's Home, He was in the middle of that Arc's Drama, but who was the Main Villain? It's the Sleeping Moria
In Sabaody too, it started with just trying to deal with Bandits & Auction House, then instantly turned into facing Kizaru & Co.
Even Marineford War with all Powerful Characters in it, it focused a lot on Akainu & He killed Ace, but then Blackbeard showed up to Kill WB
... etc
Oda didn't stop in Post-TS, SHs first encountered Vander Decken IX who is the one targeting Shirahoshi & was Wanted in Fishmen Island, but Main Villain ended up being Hody who stole their National Treasure, and again in Punk Hazard, it's literally Caesar's Arc, but didn't out of nowhere a much more Powerful Guy named Vergo show up?
Even in Dressrosa, it's True Fujitora wasn't Defeated, but it doesn't change the Fact that Oda created a Villain stronger than Doffy to share the Arc with him, and then again in Wano, most that Arc & it's Drama was about Orochi, He was the Helmeppo of that Arc, but Hyogoro summarized it when He said that Orochi never truly mattered as long as Kaidou isn't the one Killed. And look at Egghead, Oda still loves this idea of bringing Greater Villains both in middle of Arc & near it's End (And there are many other Examples i didn't mention or go into detail)
The Idea here is that One Piece have Two Main Villains
One who gonna absorb all the Drama & He is the one with a Grudge against Main Ally or Damsel In Distress Characters
He is The Evil Mastermind, and We gonna see the Dark Side of Story from his Perspective, and that's none other than Blackbeard
Blackbeard is World's Caesar or Jango or Gin or Helmeppo or Vander Decken IX or Wyper or Franky or Hogback or Foxy or Orochi ... etc
But Actual Final Villain is reserved for Final Saga to be Introduced, He is Kuro of Story, He is it's Enel, it's Moria, it's Krieg, it's Vergo, it's Kaidou
It's True He never appeared or was Part of a Sub-Plot, but his Existence has always been teased