Or maybe people have just primed themselves to dislike a character they hadn’t heard about until now, that all their worldbuilding knowledge hadn’t prepared them for, who was apparently such a crucial part of the world’s two biggest pirate crews, so they didn’t allow themselves to just sit back and enjoy this outrageous character, and so willingly see his every act in the worst light possible.
That’s a possibility too!
So, you’re suggesting that Odens appeal is apparently completely Universal, and that people who don’t enjoy him are at fault due to “rigid worldbuilding headcanon”, which made them actively choose to dislike him? Am I getting that right? Seems like a needlessly reductive and disparaging position to take regarding something as subjective as whether other people vibed with a fictional character.
Besides, Odens relationships with Whitebeard and Roger is a huge part of his character, so surely its fair that the execution of said relationships will in turn color peoples perception of said character?
Anyway, In terms of how Oden is perceived, I think a crucial factor is that his flashback is basically the inverse of the standard OP flashback setup.
Prior flashbacks have had loads of memorable, eccentric characters, but these have acted as mentors to the actual main characters, the ones from which POV we experience the flashback. In the end, the reason Hiruluk is so memorable, and that the flashback is so tragic despite Hiruluk dying with a smile, is because of what he meant to Chopper, and how Chopper is affected. Reduce Chopper to a minor presence in the flashback, and its the story of some crazy quack.
With Oden, the flashback is entirely dedicated to the Eccentric Mentor Character. Its not the Kinemon flashback or whatever, it is absolutely the Oden flashback.
And so, it is the story of an awesome guy who did awesome things, and lived his dream to the fullest of going on an awesome adventure with awesome people. Him doing that led his country to ruin, but he doesn’t feel guilty about it, doesn't apologize for it, and is not shown to be in much anguish about it. It’s the story of a guy that pretty much everyone- friends, servants, family members, countrymen, even enemies- loved, which doesn’t have time to show the guy meaningfully reciprocating the love, or commiting to even one of said bonds. In the end Oden dies smiling and content, as he wishes for the guy ruining his country to get even stronger.
How compelling. What a tragedy.
(Huh, will you look at that, I voiced criticism of Oden without it relating to Whitebeard or Roger, and I didn’t even disparage people who do like Oden, to think such a thing is possible)