I see this take a lot, and there's some truths to it, but I'd like to take the other side of the argument.
These stablecoin issuers are enormous buyers of US treasuries: "Tether Holdings owned $97.6 billion worth of US Treasuries in June 2024, a new high. Hence, Tether now owns more US Treasuries than the governments of Germany, the United Arab Emirates (UAE), and Australia. Hence, Tether is now the 18th largest holder of US Treasury bonds" (https://medium.com/coinmonks/tether-usdt-is-the-third-larges...)
These stablecoin issuers are enormous buyers of US treasuries: "Tether Holdings owned $97.6 billion worth of US Treasuries in June 2024, a new high. Hence, Tether now owns more US Treasuries than the governments of Germany, the United Arab Emirates (UAE), and Australia. Hence, Tether is now the 18th largest holder of US Treasury bonds" (https://medium.com/coinmonks/tether-usdt-is-the-third-larges...)
Dollars are also more dominant as a reserve currency in stablecoins (~97%) than they are in real-world trade (https://digitalchamber.org/stablecoinreport/).
I.e., we see stablecoins as extending dollar dominance, not reducing it.