except for the part of an economic system that requires unending growth
This is such a tired phrase. Like if we had socialism or communism or some other -ism it wouldn't matter.
But that's just not true. The issue is math and the fact that prime age working people (25-55ish) are the ones that, for the most part, make stuff. If you have a shrinking population then the % of the population that makes stuff gets a lot smaller so everyone has to be poorer. No "economic system" can change that.