@BrotherToBattle
The "Training" one is pretty damn good because it isn't about revenge at all. The party absolutely dislike the decision and they stayed friendly and on very good terms.
It's an issue that the MC simply can't keep up as he was right then. Imagine for example having your level capped at 40, then having to fight level 60+ monsters. It's suicide, simple as that.
They all knew this day was going to come and they made the hard but correct decision. Plus, the MC is much better suited to train the next generation, rinse and repeat. Which he's going to do.
His old party can still count on him and he can count on them if something arises. They're still friends. They still like each other very much.
Unlike all these rip-off thrash mangas, which is the same old drivel again and again which were made much better before indeed, like you said.