Be honest has this been done before?

Actually yes, but in a horror manga where the harem are actual monsters that actually wanna kill the MC... I don't remember the name tho, this one is mostly played for comedic effect and while they wanna kill him, he's both too strong and charms them back too kuch

Yes there's a manga that has the female healer who is actually an agent for demon lord whose job it is to break up the hero party by joining and pulling what Nagatoro's Sakura did to that group of guys

In some ways it's been done before. No gonna lie, I'm shocked this story got animated. Is it the worse? No. In my point of view, it wasn't a manga I would go out of my way to share with people.

I can't think of anything that's that specific of a subversion.

A party member that betrays you... eh, it happens. A full party of betrayers... Dunban's original party in Xenoblade lol

Yes..in to many manhwas....

imma tell my kids this was konosuba

A lot of stuff in animes has been done already. They all have similar plots.

Usually this a setup for that revenge isekai stories like Shield Hero and Redo of a Healer