Sounds like your argument is that wealth is objectively a good measure of a good life. Below some level of wealth, your life sucks, above it, it's great. You'

Sounds like your argument is that wealth is objectively a good measure of a good life. Below some level of wealth, your life sucks, above it, it's great. You're just pointing out that it's not linear, but sigmoidal. There's a range at which small changes in wealth rapidly improve or deteriorate ones life, but outside of that range, being much poorer makes your life suck only marginally more, and being wealthier makes your life improve marginally more.