> Sure, but the value of the dollar (like everything else) is in how easy it is to get (supply). The US GDP is not a measure of the supply of dollars on the market, it is a measure of how often those dollars are exchanged.

The US GDP directly translates into the amount of taxes paid. Suppose a 50% drop in the value of USD happens. If nothing else happens taxes increase by 100%, and people need to acquire more USD which drives the value of the currency up.

You might wonder about economic hardship, but historically that causes deflation. +/- 2% per year without printing money is easy, but there is a reason you don’t see huge swings without the government printing money.

> counterfeiting

An issue for any physical currency but electronic currency actually operates independently. Trying to counterfeit large quantities of cash is therefore surprisingly difficult even for nation stale level actors. A great fake bill can get passed around, 10 billion in fake bills which is still a trivial amount would trip up various monitoring systems.