I disagree. I think archetype abilities need to also be balanced between archetype as well as within them.
But thanks to clarification from other posters, it seems the capstone is powerful but not broken. It seems you get to avoid death for 1 minute, regardless of damage or failed death saving throws. This is good that they don't limit you to failing 3 death saves, because as a frontline fighter that does not go unconscious, you would continue to draw those attacks and without an opportunity to disengage, you would probably die from auto-fail death saves. But then, prior to level 15, if you didn't attack or take damage that round, your rage would end and you would die. So eliminating the death saves and capping it at 1 minute all seem to work well.
I think I like this ability now. Potent, fitting, and doesn't seem broken, at least to me.