Its kinda like a deconstruction of your typical revenge after being kicked from party.
Dude is seen as week? ✅
Girls like dude so party leader out of jealousy NTRs them? ✅
Dude is kicked out of party? ✅
We find out dude is OP in reality? ✅
Dude gets his own harem? ✅
Dude has far less issues in live, while his old party struggles? ✅
ETC.
But MC never loved the girls, they loved him cause he was mature (cause he is a damn 40+ yo isekai) and stuff, so he doesn't really care they kicked him. Hek it was more like kids leaving the nest - he saw himself as a parental figure towards them, and them kicking him out as kinda "kids wanting to go their own way".
He makes a harem of "girls his age range" who happen to be useless "gilfs" in that worlds setting, so he gets them with ease like in all typical harem isekais. Just that the reasons are a bit different. Moms of course end up being ex S-rankers, more powerful than the kids (minus MC).
Ex-team slowly falls apart, but they realize how much MC helped them, they even plan to apologise and get him back and stuff. On the way they find out that they did some shitty stuff, and probably learn from it.
So like ex team gets humbled and grows from it, MC is OP and gets even retardely OP, but he doesn't hold any grudges, and just lives his perfect milf-harem life.