Well, I had a lot typed up on this subject before by browser decided to yeeted all of it so simple, bear minimum with no deconstruction of MH's writing from my view it is.
I like the characterization of the MC as it is. I like that I gives me room to think and reflect on my own thoughts on the text rather than being told what the MC is feeling and thinking. This makes the text more engaging rather than a text meant to just be read thus it makes the text more memorable. The MC has enough character to be a separate person to myself but blank enough for me to be able to put myself in his place. No shade being through to people asking for the MC to be more characterized, it would make the text less engaging and expect less of its audience.
As someone in a Discord server pointed out, people asking for more characterization may have resonated with Pedro and the style of writing from the Hinterlands chapters. While those chapters are some of the most engrossing writings, it had limitations. The first-person perspective limited it just Pedro and we never saw the Hinterlands from the perspective of Oscar besides what he shared with Pedro. Pedro made his own choices and had his own thoughts, the only input we had over his actions was his investigation. Regardless of whether we the players had Pedro hang out with Oscar, Pedro always made the internal struggle to be a better person to Oscar. This characterization works if your audience can find something in the character to relate to but will not if they can't which is why having a self-insert makes it easier to get a wider audience step into.
No character can ever be a complete blank slate and a lot of times, most characters are not. Two VN's that come to mind are Hatoful Boyfriend and Extracurricular Activities. Both of these VN's have characters that are supposed to be self inserts, down to naming your character, but it's clear that they're their own person with their own history and personality that a lot of times don't match with the audience at all. What a lot of these games lack is a dossier on the character which can be jarring and boring to introduce at the beginning. At the same time, it is jarring to be playing a game and then something about the character's backstory is revealed in the text that is definitely not how you were picturing the person you were playing. With Hatoful Boyfriend, there's a hidden story with its own lore that's happening but I think it could have done better to establish the PC better. With EA, I like that a lot of the PC's current living circumstances are presented right away and past history comes up when it would be naturally reference but I don't like that in the beginning, I got the impression we're playing as ourselves by naming our character and picking a look for him, and I don't believe he has a family name like Hiyoko Tosaka does in HB. (It's also jarring for me as an uncircumcised man to have my penis described as circumcised as I would imagine it might be for someone with the opposite circumstance. Just putting that out there.) Maybe it's all in how PC's are introduced and setting up expectations for the player?
It's an odd balancing act. You either make a 100% defined character with a set history, personality and skill set or you make a blank slate of a person who you have to assume may not know how to tie shoes or try to do something in the middle. But as I see it, you've done an overall great job with the MC. Could it be improved in some places? Of course, just like with most writing. Maybe you'd consider revisiting past chapters and tightening up the MC a little when the story is complete a long with some other things that might be loose when it comes to releasing writing in parts.