@givemersspls
reasons I've already said.
None of your points was shown by either manga, you've mainly been repeating that 'the author could' make him a different person.
technically the author 'could' do almost anything in the story as long as they can get their editor/publisher to agree to publish it. retcon also happens too often: https://tvtropes.org/pmwiki/pmwiki.php/Main/Retcon , so I repeat your 'not set in stone'/'could' is
very negligible.
whereas, I have given points that show Urisugi is doujin MC, so I'll repeat:
two girls have literally the same appearance, personality, names and circumstances.,
the world transfer case is clearly very rare.
one more point:
None of the other males in this manga resemble doujin MC nearly as much as Urisugi resembles him:
they both have a similar smirk, haircolor, and a spiky hairstyle which covers the eyes,.
(I'm going to sleep now so I'll reply in 8~12 hours)