Imo we don't need to think about it that much, the rude stuff is mostly for the comedy and this is just a silly romcom story so for the conflict not that big is make sense to me. The constant flashback is one type of storytelling, maybe it's not your cup of a tea.
As for Yume, that's just for...
Honest? Nah this is him can't accept he does starting fall for her. I don't see any point of honest in there.
Also she's not one-sidedly receiving care? She give care to him a lot in the past chapters.
This is totally different case but i see your point. Touma would never punch her if he's here, he will punch the MC and the other bullies and then give them a speech.
You guys might be just forget, but from recent chapters, this blow isn't only about the revenge/what happened in the past anymore.
This is more of the guy can't accept that the girl now change and being so kind to him and he start to fall for her (you can see from the bubble start turning into...
So far, I don't see his inner conflict about Noona being big at all, like straight up all he thinking is what happened to Mia, why does she changed, etc.
From the beginning it's so clear he's never forget and go over his feelings for Cha Mia.
I will say the wrong is on the plot he's in love with the senior.