A major problem is that the poorer you are, the higher your deductibles and copays because the crappier your health insurance.
A person making 120k a year probably has much better health insurance than someone making 40k a year, because the employer paying 120k a year is willing to pay a few extra thousand a year for a higher quality health insurance plan. the more money you make in wages, generally the better your benefits. Also the more money you make, the easier it is to pay for copays and deductibles.
This means that the working poor and lower middle class have insurance that they can’t actually use.
One potential way around this is some kind of federal cap on ‘all’ health spending as a % of income. Something like 10%, meaning that everything above 10% of gross spending has to come from public subsidies. So if you make 40k a year, then you can’t spend more than 4k a year on premiums, deductibles and copays in a year. Everything above that has to be subsidized by the public sector or your employer. This is one way to get around underinsurance.
But another plan that could work is called ‘medicare extra for all’. Its not medicare for all, but its a more advanced form of medicare that anyone can buy into. Its more advanced since it would cover things like dental, vision, hearing aids, etc that regular medicare doesn’t cover.
https://www.americanprogress.org/article/medicare-extra-for-all/
Premiums would be like the ACA, they’d be capped as a % of gross income. But also deductibles would be tied to gross income too so that you don’t end up with people making 20k a year on a health care plan with an 8k deductible.
Also all uninsured people would be auto-enrolled into medicare extra, which would mostly eliminate the uninsured.
So medicare extra for all would largely eliminate uninsurance and underinsurance.
Medicare extra for all would cost roughly 300-400 billion a year, most of which could be funded by savings on health care, and higher taxes on the wealthy. However a small payroll tax may be necessary too (a 1% tax added to the 15.3% FICA tax would raise an additional 130 billion or so a year). However medicare extra for all could be a bridge to a health system like they have in Australia. In Australia they have medicare for all, but you can buy private insurance on top of it. That would be the end goal, a system like Australias.
https://www.americanprogress.org/article/medicare-extra/