Take it from one who departed a mainline many years ago for their use of hard-earned tithes on blasphemy....God cannot bless the apostate churches.
I understand your argument, but just don’t buy it. I feel the same way about people who leave their children in failed experiments called government schools because their kids “need to learn to stand up for their faith in this world.” As if a 7 year old (typically not yet saved) can or should be asked to do that.
No, I have one word for these situations - flee. Find where God is working and join Him there instead.
But the difference between this and the situation that you state (gov school) is that the Church is not just a school where you abide your time. The Church is THE Community of God, Our Family. We don’t abandon them, even if they make mistakes. If it is being destroyed by a weird cousin , then the apostate gets pushed out, not the orthodox.