No it's about power to an extent, but Roger did not become the PK until he circled the world.
Notice how he was called the King of the Sea not for his strength but circling the globe?
What is Haki going to help then? They use guns and devil fruits. Pre-ts Zoro loses but now it's different. BB would destroy Magellan. Would Magellan beat guys like Garp or Sengoku then because they aren't immune to poison? You say to me, Zoro has no immune to posion or gas and neither do Sengoku or Garp. All they got is their fists.
Haki protects swords from breaking and by extension....melting.
That small protective film isn't poison proof. Zoro can use his bandana, just like Sanji has with his small mask.
I never said he needed everyone, I said what happened is unknown. Because we don't know how Shiryuu got imprisoned. This is all we know:
See how Ivankov uses the word "they" which is plural. Not "he" as he would if he was referring to a single person.
Your turn, show me where it says Magellan beat him in a 1v1 and it was less than a high difficulty fight.