You could argue that the message is a lot more positive and healthy than most power fantasy isekai since here despite its genericness the emphasis is put not really on the power fantasy but on Yuuya, the protagonist, being rewarded for never letting his bullying and overall shitty life turn him into a bad person and staying at his core someone who will help others as it is ultimately an act of kindness at his expense that makes his life in the real world get better, even if over the toply so but hey this is an isekai. And honestly all the power to the story for it. If you're a down on your luck lonely person there is a certain catharsis in seeing him becoming a badass, his life getting better, people respecting and admiring him, all the while staying the same good and gentle person he always was. I would love to do that, but the power fantasy aspect inherently cheapens that.
Yuuya doesn't really resolve his low self-esteem because of his conscious effort to better himself it kinda just happens because people like him now. The betterment in his life is simply due to him being a good person and also non negligibly being lucky enough to have a door in his house that led to another house in another world filled the absolute peak of materials and weaponry.
Also, it just so happened that he encountered a powerful monster that he defeats accidentally because his weapons are just that op.
And also, it just so happens that levelling up turned him into a tall handsome hunk.
And then suddenly his life started to get better.
Remember Mushoku Tensei and Faraway Paladin? Well in those stories the protagonists also grapple with self-worth but to become powerful they had to put in considerable efforts. And even then, it doesn't magically resolve their problems, they also have to put in great efforts to become better people, grow and gain confidence. It's a constant deliberate effort and they often catch themselves falling back into their old habits. None of that happen with Yuuya, the moment he levelled up and turned into a hunk suddenly his life in the real world started to get better, people really liked him because he was handsome now, he didn't even really have to deal with his bully as a pretty rich girl he saved from hooligans when he had yet to become a hunk literally arranges for him to attend an elite school where everyone just like him because of his new specs, all in front of those bullies for that little bit of serves you right moment. For Pete's sake at one point he is even in the cover of a magazine as impromptu model because he is just that handsome. None of that is due to his effort, events out of his control favors him and now his life is better.
So basically, karma will solve your problems for you so just wait and be a good person. I know that that's not exactly what the story wants to be about but it handles its themes of self-worth and overcoming your insecurities so poorly that that's how it comes across. Ultimately, I could only see myself recommending it if someone just wanted a mindless feel-good power fantasy because honestly otherwise it's just a generic isekai. And those very aspects that may have made it a guilty pleasure slowly fade away to be just a generic power fantasy. So honestly it may very likely reach a point where I can't even recommend it for that.
