> If everyone is deficient, then it must not be that important.

Most people are overweight. Does that make being a healthy weight not that important?

[dead]

most people can tolerate being overweight pretty well it seems

Not according to the public health literature. But, hey, don't let hard population data spoil what things "seem" to you.

Here are a few highly-cited articles to get you started:

https://link.springer.com/article/10.1186/1471-2458-9-88 https://www.nejm.org/doi/full/10.1056/NEJMoa1614362

For what definition of “tolerate”?