I'd be interested in the exact reasons people are icky about the potential relationships. People I know are massive fans of Flowery Path of Evil and at least the age gap there is much bigger so... Surely it can't be that, right?
Flowery path of Evil makes for a pretty good comparison when you consider people's reaction to its sequel chapter.
FPoE Original one shot: MC is forced to marry a fat old man and they end up very happy and evil and glamorous.
Most of this chapter: MC is a realistic and responsible teacher who cares about his students
A lot of people like this because those concepts are interesting and unusual
FPoE Sequel Chapter: Focuses a lot on MC's handsome stepson being in love with her and hoping he could marry her after his dies.
This chapter ending: One of MC's students falls in love with him, everyone accepts this, and MC's just like Ohhhh noooo
A lot of people are disappointed because the unusual concept they liked got undermined in favor of something they see all the time in other stories.
I wanted to see more of MC and her evil old rich noble husband, get that generic pretty boy out of the shot.
I want to see more of MC being a responsible teacher, stop setting him up with one of his students.