The first few chapters spent a lot of time setting up a revenge story
No it did not. Compared to others in similar theme its rather cut short. Read some more isekai in similar revenge theme. btw how is this even an issue? (nitpicking obviously)
They also spent time building side characters
Wich is a good thing.
MC is ostracized due to generic reasons, and that everyone he first meets are either sheeps or people created for the soul purpose of being hated by the reader
teens die almost daily cause of suicide. Sorry that it's generic for you. everyone he first meets? nitpicking much?
MC Gets sent to a very high level dungeon, and finds the mcguffin that turns him OP
ever heard of an isekai manga where the guy kills an army of high lv lizardmen with a meteorite and after the lv up gets to be a god? Yeah that even got an anime adaptation. Again nitpicking.
MC beats a mimic with his new power showing it's OP
What is even the problem?
Leaves dungeon.. somehow by using magic stairs... shut up it makes sense!
again what is even the problem? Its a fantasy magic isekai. Nitpicking yet again.
Welcome to the world of adventure mangas.
Rest of chapters is MC gallivanting
You watch too many Game of Thrones. And stop nitpicking little Theon.