"Death of the author" is meant to give you the option to find your own deeper meanings in a piece of work. The hidden symbolism and messages. I don't think it was meant as a way for you to just prefer alternative facts, which I feel is being conflated (because you're talking about character strength).
If you look at any piece of art, fandoms (including casual and hardcore) take on a life of their own and will congregate on specific viewpoints about that work. Or any large community, really (e.g. Conservatives and Liberals in USA). I don't think the specific viewpoints the communities lands on are necessarily the most "correct". Especially in something like One Piece, where the ambiguity on certain things is by design. By factors outside of the story (e.g. how many people like a specific character, how many people are biased for or against specific agendas, etc.), the community hive mind will make their decision on a specific topic and roll with it for years. As long as it's plausible and pushed, of course (Sengoku has no fans to do this for him lol). On the other hand, nuance and minority opinions get weeded out. To a certain degree, the specific ideas that the community at large settles on can be pretty arbitrary and coincidental.
The "average" community opinion on any given topic is not guaranteed to be superior to a random fan's. In a different universe with the exact same manga, the community's conceptions about the story will differ slighly by pure chance. In that universe, more people might've glazed Mihawk, and the "casuals" you're referring to might've been fed a completely different worldview through their algorithms, influencing their thoughts in a different direction.
Just compare the English-speaking and Japanese-speaking communities for One Piece. Because of the language barrier, the hive minds had a chance to develop separately. Do both communities land on exactly the same opinions on every given topic? Do they scale every single character exactly the same in relation to eachother? I don't actually know. If someone has insight into this, feel free to share. I would assume they power scale similarly to a certain degree, but some characters do better or worse in one community or the other. Similar to the popularity polls. But it's hard to get a read on the "average" power scaling tier list for the Japanese fandom. I've only ever seen two lists, and they were completely different to each other.
If it's the case that there are differences, and I would bet that there are (e.g. maybe Japan glazes Rayleigh way more than the West, I don't know), that's not an author problem to me at all. Actually, it's not even a problem to me. I don't get why you're so bothered by this, to be honest. On a personal level, I read One Piece for decades before ever getting into community discussion. And when I did, I got surprised by the community consensus on certain topics. And I still disagree on many of those things. I'm sure that many people experienced the same thing. And my opinions also get updated like anyone else's. I don't feel "scammed" by Oda that the community might be wrong on some things, because I never agreed on many of those things either. And I always recognized that I could just be perceiving things incorrectly. It's kind of moronic to think you got scammed, because it implies that no one else could have landed on the same conclusion that the author is putting forth. You talk about circles where Mihawk was downplayed, but in my circles he was gauged more correctly.
From my point of view, you're coming off a little salty that you might've been wrong about a specific perception around Mihawk and you're attributing it completely to the author, ignoring that maybe your own perceptions, motivations, and influences (who you specifically hung out with if not the wider community) are actually a bigger contributor as to why you're feeling scammed. There's nothing in this story to indicate any issue with Mihawk>Shanks (or the vice-versa) in a completely objective sense (at least not yet). Your mistake was simply thinking the community hive mind = truth instead of just one interpretation. And maybe reading a little too much into aura. It's really not a big deal.
As for whether I see an issue with Mihawk: no. I recognize that he lacks aura (and I have ideas for why that is), but it wasn't always that way (and it's slowly being rectified in the background). Unlike many other readers, I had the chance to linger on and think about early One Piece before any Grand Line content even existed. During that time, Mihawk was cemented as a top tier in my mind as his only competition was basically just Shanks, Dragon, and Roger for characters that could be considered to match or exceed him. Other top tiers didn't exist for years.
And my take on Marineford was that it was about introducing the Emperors (+ their crews) and Admirals first and foremost. There's no point in glazing Mihawk during Marineford. Mihawk was already a known quantity and it was more crucial to give focus to other characters. His motivations didn't line up with taking a front-and-center role, either.
I actually think that's why there's a divide on this character. Readers who started only during/after Marineford basically had no time to think of Mihawk as a top tier during their binge to catch up, while those of us who had been reading for longer already had him cemented that way in their heads. Clashing with Vista for a hot minute wasn't going to change that for us. So Mihawk being a "background" character in Marineford probably contributed to his lower perception among the modern community of today. And, similarly, if you start and catch up to One Piece today I think you'd naturally rank Mihawk higher just because of Cross Guild's intro and all the swordsman pulling up to the final saga. I don't see a problem with any of this. It's all arbitrary perception.