What does height have to do with fitness? That analogy would be relevant only if you had a normative notion of height in mind. For example, if you were scouting for a basketball team, you'd be looking only for players who are, say, over six feet tall. So the candidates would have to fit that mold or ideal.

The question you pose is fine, and I'd like to see you try to answer it without presupposing an ideal that makes the harmony normative: What is the way humans might fit with the rest of the world? Would fitness require happiness or material or romantic success? What cultural standards would we have to presuppose to answer that broad question of human fitness? Biologists talk of genetic fitness, so maybe we'd need to incorporate that. Or maybe we'd presuppose neoliberalism or some American individualism.Perhaps we'd side with collectivist cultures and reject individualism as infantilizing.

Wherever we go for the answer, we'd run up against the naturalistic fallacy. Vervaeke might say that we tend to assume happy people fit better with the world than sad ones. But the fact that we tend to want to be happy doesn't mean we ought to have that goal or that that goal objectively matters more to the universe than does some other one.

On the contrary, we might assume that happiness (contentment) is for infantilized suckers, and that the more enlightened path is to cherish alienation as a sign that we understand how anomalous our species is, and how much we stand out from the universe, as opposed to fitting into it.

I reject Vervaeke's whole Taoist, Neoplatonic premise as being all too consistent with the dubious happiness industry.