Why is average wellbeing a goodharted measure?
Offing those with low wellbeing increases average wellbeing.
That in itself can be solved (if you break the symmetry between killing / not allowing to live), but it still remains that a tiny super-happy population (of one person in the limit) is what’s aimed at.
It ignores many important aspect of human wellbeing:
1) preference to stay alive, even if it is unpleasant + some other preferences
2) time relation between observer-moments: e.g. short intense pain is not very important
3) non linear preferences about intensity of pleasure and pain. people could work a lot of time for short pleasure
4) social values (family), intellectual values (knowledge, diversity of experiences)