Leaving the US is funny, its like a ex that won't stop calling and harassing you. The US wants its taxes first before any other country collects. If you try to permanently sever ties, its a long expensive process.
FEIE as an example is a deduction that currently goes for around the first ~$120k you earn, you also have your standard deduction. This only applies if you have spent at least 11 months in another country. Then there's housing, foreign tax credit, and so on.
In reality, most expats who earn any sort of income pay $0 to US. The only requirement is that you file every year, like all citizens to the US. Double dipping, like you're alluding to pretty much does not happen much.
Relinquishing citizenship has a fee of $2350 minimum attached to it, which is hefty, but if you're giving up your citizenship, chances are that the bill is paltry compared to your supposed other benefits.