I mean, Brigitte needed some kind of nerf. Maybe. But giving Rally decay kills the uniqueness of the ultimate. It’s 30 seconds, sure, but it still doesn’t make much sense (outside of preventing Zarya, Zen and Symmetra abusing it). Chipping it off was not a problem - a rocket/grenade or two, a half-charged Rocket punch, a few revolver shots, anything - and it’s gone. Not to mention it takes more ult charge than Transcendence, one of the two all-saving ultimates.
Armor nerf in general might have been enough, especially since (according to Overbuff) Brigitte is already the least picked support across all ranks except GM. This will only make sure Brig is never played again. She is the worst at solo-healing, a questionable pick as a second support, and only good as a third healer.
I don’t play her much, but please, don’t Doomfist her. This might be the nerf she needs, but not the one she deserves.