But in this case arent there are objectively better subjective value hierarchies to seek than others?

In your statement "for society to even function, we have to ultimately have some shared subjective assumptions"

Wouldn't you consider seeking the ones that create the best functioning societies to be ultimately objective? Or is 'best' too subjective there?

I guess I consider seeking 'truth' as seeking one with the most productive, fulfilling, honest for oneself without encroaching on other people on their journey to do the same. I believe this because over the long run, it wont only be better for my future self, but ultimately a better society at large.