US Nominal GDP is priced in USD - for you to claim US GDP is 'fake' is functionally labelling the USD as overvalued. This is not a strawman at all.
By your logic, Goldman Sachs and Lockheed Martin are...absolutely not part of the US economy.
How does the USD have the backing of the US military when you apparently believe the US military has no technical edge? Every country can claim to 'back up' their currency with their military but why do countries only acquiesce to the US?
You asked literally the dumbest question ever - if the USD is correctly valued then 17T $ economy is correct. If the USD is OVERvalued then 17T is obviously understated. If the USD is UNDERvalued then the economy is less than 17T.
What you and
@Serb do not seem to understand is that for all your beliefs about the Chinese economy to be true ('uNdErVaLuEd'), then the Chinese economy, quoted in USD terms, will need to rise to reflect all these supposed 'undervaluations' via USD depreciating (in other words, USD losing purchasing power in RMB terms). Otherwise Chinese people will continue to suffer weak purchasing power globally via services (of which China is a HUGE net importer).