Except here is something you didn't know - that British citizen isn't paying income tax at all. Their 0% bracket goes all the way to about $16,000 USD Today. That US citizen is paying about $1650 in income tax because there is no 0% bracket in the US. So in actual take home income they are almost exactly the same. The mess of tax code in both countries makes the calculations more complicated, plus other taxes, etc - but the point is that no, U.K. citizens are not being paid "so much lower" than the US on average, but they do get the benefit of never dying of preventable illness because they can't afford to see a doctor while having all that extra aforementioned paid time off and holiday benefits that US workers don't have.
Additionally, the US isn't even at the top of median individual income. Fennoscandia collectively has the US beat, by on average about 20%. Which is going to be offset by their average ~25%ish income tax, but still its comparable returns.
It turns out that if your economy is abusing you to get more productivity out of you that you don't get a better living out of it.
I made ~$80k USD and because of various tax incentives (3 children mainly), I paid almost exactly the $1650 ($1683) figure you mentioned for federal income tax.
So my intuition is that the tax burden for most poor families is almost nothing.
I would expect self reported income like that to be based on take home pay (so after taxes). And for many in the US, they will have health benefits that they don't include in the self reported figure (they may not even realize the amount their employer pays). That's hard to account for compared to the "everybody can use the NHS" included in the UK figure.
Untrue for Sweden[1] and Norway[2], which have respectively 14.3% and 16.8% of their populations foreign-born. Not all of those foreign-born are from developing nations but developing nations figure heavily in the top-30 list for Sweden.
1. https://en.wikipedia.org/wiki/Immigration_to_Sweden#Demograp...
Norway is not significantly different when looked at in a similar light.
So why are salaries in the U.K. so much lower than the US?
Seems like the only one paying for holidays is the worker.