I have thrown people under the bus while under pressure from my manager to explain why reviewing a Pull Request takes me several hours or days while other members did it in a few minutes. It was the wrong thing to do but the pressure was unbearable.
Combine the current job market with, say, a work visa tied to the employer, and it turns out "just" in "just leave" does a lot of heavy lifting...
Sure, but so does the word "unbearable." If your workplace is unbearable, you will probably need to leave sooner or later - either because you found a way out or because you burned out. Whatever GGP did might've saved their hide, but it probably didn't result in a "bearable" level of stress (indeed, they said it was "wrong", so it probably gnawed at them). Stress has a way of diminishing your capacity when you need it most. Better to act sooner than later.
I appreciate your honesty, that's not easy to admit even on anon forums. You seem to evaluate it correctly. Just one thing - if work is such shit ie due to manager, just leave, you don't own them nothing. First try to talk to manager that this doesn't work and what can be improved to bring out your potential, but in any case search of another job should run in parallel.
I've seen so many brilliant people stuck in jobs they didn't like or even hated, when it would be trivial for them to stand up and go to next door. Yet they didn't. Don't be that guy.