I'm not sure where you're getting the $20,000/year healthcare spending number, but that looks like it is too high by an order of magnitude. See e.g.
https://www.commonwealthfund.org/publications/issue-briefs/2..., which puts median annual household spending on healthcare between $1,500 and $5,540 in 2019. If you're talking about total annual healthcare spending, that is largely paid by employers so should be accounted for as increased gross earnings for employees, which translates to lower effective tax rates.
And yes, the effective federal rate is not the total blended rate paid in the US, but it's not in the UK, either. For example, far as I know, no US region has a sales tax close to the UK's 20% VAT - sales tax is set locally but in most places is around 5-10%.