It seems like for health insurance at least, the problem of trying to optimize insurance premiums based on any risk factor you're legally allowed to discriminat

It seems like for health insurance at least, the problem of trying to optimize insurance premiums based on any risk factor you're legally allowed to discriminate on is a problem that just sort of goes away in a medicare-for-all style single-payer insurance system. Everyone pays taxes and receives health care services -- you just have to make sure your taxes rate is set properly to cover the costs incurred. (I think governments are sometimes unfairly criticized for inefficiency because they incur higher costs simply by not having the option to cherry-pick their customers the way private companies usually can. There are of course cases where the criticism is justified.)