This is a linkpost for https://atheistkit.wordpress.com/ethics/
You are currently saying that the good is what people fundamentally value, and what people fundamentally value is good....for them. To escape vacuity, the second phrase would need to be cashed out as something like "side survival".
But whose survival? If I fight for my tribe, I endanger my own survival, if I dodge the draft, I endanger my tribes'.
Real world ethics has a pretty clear answer: the group wins every time. Bravery beats cowardice, generosity beats meanness...these are human universals. if you reverse engineer that observation back into a theoretical understanding, you get the idea that morality is something programned into individuals by communities to promote the survival and thriving of communities.
But that is a rather different claim to The Good is the Good.
Clarification please. How do you avoid this supposed vacuity applying to basically all definitions? Taking a quick definition from a Google Search: A: "I define a cat as a small domesticated carnivorous mammal with soft fur, a short snout, and retractile claws." B: "Yes, but is that a cat?"
Which could eventually lead back to A saying that:
A: "Yes you've said all these things, but it basically comes back to the claim a cat is a cat."