I agree that one unified stat seems limiting, but even 1 more would add lots of simple depth. Lots of binaries to choose from (physical/mental, detachment/attachment, instigation/reaction, etc.) that I think could be used to still represent the ways in which people are affected by a sort of crumbling world.
I think I may not have been clear - I was planning on using other stats too - just using Ruin as a unified measure for physical/mental mutation. My rough draft is Impact to measure smarts/strength and Survive to measure toughness/agility.
While I'm not 100% convinced it's a good plan, it's the one I have and am going to work. I suspect that, in the end, forcing the choices is a great thought experiment but maybe not the most playable game. We'll see.
Leaning into the story structure though - that I do think is worth exploring.