USD is important.
Cross-borders transactions are mostly in US. Try changing TWD directly to KRW in Korea, I think the spread is more than 10%. Commodities are priced efficiently in USD, otherwise the spread is wide.
Then the whole NASDAQ and NYSE trades in USD, total market cap of companies in these two exchanges alone are over US$200 trillion.
Then came the cryptocurrencies that created so much artificial wealth of thin air. Again, they are valued over US$4 Trillion and mostly priced in USD.
Last but not least, China may be buying more gold but almost every G7 country has more gold than China. The gold reserves held by US is like 30% of the world's central banks' combined. Now Gold rocketed to US$4000 per troy ounce and this is another astronomical gain.