IMO Luffy vs Lucci was extreme diff, Zoro vs Kaku was high diff but not extreme diff. I agree Sanji vs Jabura was mid diff. But the problem with doriki is that, if Luffy is exactly that much better than they are, logically he should not have had a significantly harder time with his opponent than they did with theirs, idk if I'm saying that right.
Regarding Whiskey Peak, I think it was clear in the panels that both Luffy and Zoro were serious DURING the fight, and they both seriously declared that they wanted to see which of them was stronger.
Other than that, I don't necessarily think there are moments where it's explicitly implied that Luffy = Zoro, but I do think Luffy and Zoro as a DUO appears with similar prevalence in the story as Zoro and Sanji as a duo. Zoro is the only SH to fight shoulder-to-shoulder with Luffy in battle, even being described as Luffy's "partner" by Smoker, etc etc. We can get into supernova stuff and dreams/ambitions and whatever but that stuff is more trivial. I don't want to add too much detail because I don't actually believe Luffy = Zoro, but my point is there are elements in the story that pushes Zoro as Luffy's "partner" more than anyone else in the crew, while he lacks that type of development with Sanji in my opinion
On top of that, we do have direct confirmation from Oda on multiple occasions that describe Zoro as the no. 2 of the crew, which is why I choose to just abide by the logic of Luffy > Zoro > Sanji without digging too deep into the gaps. Obviously Sanji is a beast and IMO neg diffs the other members of the crew besides Jinbe even though he still beats Jinbe by a landslide at this point