Author here. My manager and I discussed lengths about the capabilities they do, and it is just like this. It's not his fault at all. It's a game at the end of the day, and it's your choice whether or not you want to keep on playing
Do you think retrospectively your manager may not have been as supportive of you as you had thought?
You missed promo 3 times, and when you left he didn't try to counter you. Is it possible s/he might have been blocking you?
Having been at G and also getting denied promo several times consecutively, it's almost always a manager's fault. They're either not bringing the committee feedback to you properly or not representing your work well in that room. Either way it's a sign that they're unable to do better, and you're better off not reporting to the long term.