The issue is that all of the other characters are bland and uninteresting.Just get over it already... The MC is NOT the only important character in this story. The other classmates (plus various other parties) all have important roles. In some ways, this is like a Battle Royale with competing characters with competing interests.
It's ironic that we get a story where the MC is not some Completely OP Self-Insert... And then we get people complaining that he's not a Completely OP Self-Insert. /SMH
The only saving grace of a series like this is the conflict that's introduced in the MC being thrown away. If the author had any skills in writing actual people instead of cardboard standees it wouldn't be a problem, but so far the only interesting people are the MC and the cheetah lady (well, and pigimaru too).
I've had to work on plenty of these kinds of stories as a PR/TS/QC and it's the same major issue they all have in blowing up the small amount of story/concepts they have without any consideration about actually developing a setting with a proper cast.