Your 1st half sounds reasonable but wow its amazing how full of schizophrenia your 2nd half is, headcanons and projections about something thats not even related to the topic at hand.
'You're obsessing over this too much, its unhealthy' is certainly something that you should apply to yourself as well because those otakus certainly have nothing to do with the topic but you felt the need to bring them up.
Actually, its not unrelated. The concept of the self-insert and a cultural commentary being embedded into a manga by its own creator. I am not the first and only one to talk about such a concept on this forum. And actually, some people have already concluded that this is the case, whereas I myself am still "feeling it out" and trying to understand what it really means if it is indeed all true, what lessons I should draw from it.
If you recall some past discussions from, for example Oda's SBS, he at times indicated much of the manga consumer culture has a demand for very well drawn characters, articulate fight choreography and I guess by inference emotionally moving plot lines with moral and romantic themes. (Especially romance between young, good looking teenager type characters and the like.). If you read the discussions like that where Oda actually commented, he did not speak in such a way as to indicate he was too pleased with the demands of the consumers or fans, if you will. He wrote of it as something he has to deal with, not as an expectation he personally enjoys satisfying.
So, when Oda subverts an expectation for either art, or poetic and moving storylines, or some other with a version of the manga that seems intrinsically different in some ways from say, the pre-timeskip era... it's not guarenteed or a given that its "out of no where" as if its something forced on Oda by editors or whatever. It's literally out of the author himself. Consider the development of the character designs. Oda did not always draw the characters the same way. When One Piece started, the art style was quite different than later chapters. Is that an adaptation that Oda made perfectly willingly, or out of necessity to satisfy cultural expecations and thus to be successful in maintaining an income?
The commentary of how Oda's idea of "Now I can do whatever I want" and how it relates to, say the radical Otaku culture, is that Oda obviously has not indicated a great deal of loyalty to many of the Japanese philosophical writing concepts and their expectations imposed that would be reflected in what we might call "higher quality scenes" as we perceive it. Have you ever grasped the concept of the "Now wealthy" business owner who begins to openly disrespect and disparage his own workers because he has reached a point where he can do what he wants and get away with it? You would conclude, nothing changed except the fact that he could get away with it. The desire and will was always there, just not the political immunity. What I am implying is obvious. There are a group of manga consumers with high expectations for good art, certain story lines, and ideas of how things should happen based on common Japanese cultural norms that are frequently used in an almost formulaic way in manga, and it is quite possible that Oda is intentionally rebelling against all that.
So even though we might have people who hate the "Tom and Jerry" art concept, and have this idea and say things with personal anger like "Why the fuck is Oda dabbling in the Westernized art style that looks like shit, and is goofy as hell" - there is a lot of evidence to bring up
suggesting that Oda never shared the same obessession with Japanese culture that some of the readers did. Part of that culture is absolute seriousness in their work ethic, especially with a view to art and spiritual philosophy, and obviously drawings by inference. Remember, Japan is a nation that has been known to even treat tea making - literally, tea making - the most idiotically simple act of pouring boiling water into a cup with a tea bag - as an art. They are known worldwide for seriousness, and treating things as art and sharing their moral philosophies in stories that often share the same themes, despite having very different authors.
Consider Armstrong's commentary on the Cherry Blossoms in Metal Gear Rising for example.
Armstrong is obviously seen as "The American view" of Japan, and the people who supposedly call the cherry blossoms "fleeting and beautiful" are seen as representative of Japanese thought - but that's just an absolute caricature, of course. Many Americans are now obsessed with Japanese culture and manga, for example, and some Japanese dislike those elements of their own culture because of a perceived over saturation. "Too much of anything, even good things, is unhealthy".
Don't you think that Oda might hate the idea that every single Japanese manga looks in some intrinsic way, the same, when it comes to art quality, fight scene expectations and moral themes? Is it not possible that he might hold disdain, and view it as soulless and repetitive, a mere formula that is repeated and exploited?
For another example, consider the Gundam series. I love it. I find it very deep, and the art is awesome.
Yet at the end of the day, is there not a good argument that despite all moral themes and art quality, Gundam is just an excuse to sell overpriced toys and merchandise?
I am sure this concept is relatable.