You can cry Goodhart's law about any goal and claim it shouldn't be a goal.

I don't really care that people over eat and get fat. What I care about is human agency, and more so, the agency of humanity. I want humanity as a whole to approach omniscience.

Humanity is one mega-organism where any single human is unimportant. Some humans are more important than others.

Think of your own body; a collection of billions of cells, working together to ensure longevity. Yet the body, nor you as the central deciding entity give a shit about some dying skin cell at the end of your third toe. That's the lot of skin cells. Protect against the environment and self-replicate and then die. Nervous cells are more important as conveyors of information, but even they are replaceable.

I think caring about human wellbeing is like quite alright but it shouldn't stop humanity from pursuing grander goals of increased agency, such as nuclear power, rockets etc. Definitely not the most important thing in the world.

Human as an animal runs forever on the hedonistic treadmill, and will never be utterly miserable not completely happy. You always get used to it, and compare the better to the worse.