Technically, Luffy's aiming to be the Pirate King, and they would need to surpass the general Yonkou level to do that. This would be the arc to place them on the level of a Yonkou crew.
Zoro's end goal is implied to be Yonkou tier, so now would be a good time for him to hit YC1. Sanji's EoS fight is up in the air (hopefully an Admiral), but either way, he'll be ready after fighting King or Queen.
But Roger was never implied to be stronger than the other top tiers. His fight with Whitebeard is a tie, both are stronger than Oden and Rayleigh but Oden and Rayleigh are also subordinates.
The power hierarchy back then isn't much different from what it is like now. If anything, Xebec is a step above the others.
There is no world in which Oda could make Sanji beat an Admiral. The Admiral's and Yonko are the same, that's as strong as you can get and as such reserved for Luffy alone. Beating an Admiral would require a 20 chapter focus, that's not going to happen as a 1v1 for Sanji or any other Strawhat for that matter.
The way I see it, many people look too much at the "Dragon Ball" concept of powerlevels when evaluating Shonen, because One Piece doesn't really work like that.
Goku, the protagonist of Dragon Ball, always wins by being the strongest. If the enemy is stronger, Goku gets a new power-up or move to succeed.
Luffy, the protagonist of One Piece... well he (almost) never wins by being the strongest. It always comes down to circumstances.
I discount Arlong since here it was LUffy's own stupidity, but afterwards:
He lost against Crocodile once and was saved by Robin, lost again even after discovering the weakness and was saved by luck, and then only beat Crocodile after his plans were ruined anyways.
Enel got hit by a Reject Dial before, which otherwise defeated Shura in one blow and created a giant hole in the Giant Jack. During the fight, Enel threw Luffy offboard after encasing his arm in gold, then proceeded to destroy Skypea, which would have killed everyone, including Luffy. Luffy then needed help from Zoro, Wiper and Nami to move up the Giant Jack to defeat Enel.
You can discount Lucci as an exception, but this was a villain specifically designed as a measurement stick, as Luffy's equal with the whole Doriki stuff and such.
Luffy had 100 shadows infused into him to defeat Oars.
Luffy required help from Shirahoshi and the Fishman to defeat Hody Jones. Luffy has a disability here, after all.
Luffy required help from Law and the Colliseum Gladiators to defeat Doflamingo.
Luffy had help from Brulee (lol) against Katakuri and in the end only won via special circumstances and deep mental stuff inside Katakuri.
The fight of Luffy vs Katakuri is also a good example of how power-ups in One Piece work. They are always mentioned in the text or explicit artwork and happen at natural points in the story, but they are not Super Sayan. Luffy powered up his CoO during the fight but it was still nowhere near enough to defeat Katakuri. It only pushed him one step ahead of were he previously was. He was "weaker than Doflamingo" before and became "weaker than Katakuri" during the fight.
Now he trained his CoA and as such is one step ahead of were he previously was, he is "weaker than Kaido" now.
The Yonko and Admirals are the max level, they are the top end, as strong as you can get. Luffy will be at that level at the end of the story, during the final arc, but this is only the penultimate arc, meaning he will defeat Kaido via circumstances as usual and it is already shaping up like this with the Scabbards already fighting with Kaido and the other Supernova set up as well.
If Luffy will be at that level at the end, that means all of his subordinates will have to fall below. That's why I think Sanji's endgame is a Titanic Captain from the Blackbeard Pirates, and that will be true for all other Strawhats except for Zoro, who might face Mihawk.
It all makes a lot of sense like this, the Strawhats become an endgame pirate crew in line with the others at the end. Becoming Pirate King is not a feat of strenght, it is an entirely special feat and Luffy becomes Pirate King because that is the plot, he is the special one that pulls up special things as he is the main character of this story, and in the end it is a story about being special and not about being the strongest. The way things shape up, Luffy will also defeat the WG not because he is the strongest, but because he has the ability to gather friends and allies from everywhere.
They admitted it, Oda and Animators hate Sanji.
<<Sanji will never look as good as he did before>> pre-timskip days of Sanji were his peak.
Pls stop. That's not really what is said there and Oda isn't even involved.
