So dungeon stuff happened not that long and people are already at wars for what seem like for years.
Characters have 1 dimensional personalities and are very boring.
They had grudges before the dungeon stuff, but now they have powers so they can act on it. And clearly both are gang/yakuza type characters.
Also, the only people with 1 dimensional personalities are the MC and Sol. Mostly because the MC is being written as a bit more stoic, thus a bit flat, and the kid is basically a newborn fawn. (Also because the MC can be a medium for the readers to self-insert and be immersed in the story from the original novel's format. It would be odd to change the established character just because it's now a manga.)
Another thing is, this Tomoe character is clearly intentionally built to be a cardboard cutout because she's a cloned zombie designed by the villain (I assume.)
If you've been paying attention, the other characters actually have their own motivations too.
Murasame is a yes-man... but still lets her opinion known (the tl was all over the place so idk if trap or messed up pronouns), she clearly doesn't approve of her sensei involving the outsider(MC) but she'll follow orders (literally in the titles). Despite her standoffish attitude she's determined enough do things outside her comfort zone (like being a teacher for kids) to achieve her goals and she even sympathizes with Chake, a seemingly pathetic crybaby despite what her first impression might suggest.
That girl that had her house destroyed and her family killed is expectedly depressed and mourning, so her character changed massively.
The girl that likes the MC is genuinely just trying to make do with the situation despite everything, caring for the others when she should also have her problems. She's not just a one note character that's just there to do heart eyes at the MC for every scene she's there.