Your last paragraph nails it.

Not an economist either but from an international perspective the MMT/Kelton dEfIcItS-dOn'T-mAtTeR stuff really does boil down to American Exceptionalist propaganda.

It relies *a lot* on the TINA assumption ("There Is No Alternative") and lacks a coherent theory for how to deal with its inflationary effects. It also disregards the interests of the very foreign creditors it relies on (i.e. the governments, businesses, investors, etc buying the $10Ms in bonds in your example) for all that money it advocates printing to retain its value/reserve status.

I mean there's the Euro, the Renminbi, and for those who believe fiat currencies as a whole may fall out of favor... cryptos are attracting more and more institutional investment (and foreign government exploration) as we speak. Plus, old faithfuls (eg. gold) will forever remain in the mix. So imho TINA is dead and it's not a question of if the US dollar loses supremacy but when. As a share of the currency composition in official foreign exhange reserves, the US dollar's already declined by over 10% since 2000 (https://data.imf.org/regular.aspx?key=41175). It is not at all beyond the realm of possibility that foreign creditors dump it at an accelerated rate.

Reckless deficit spending, rapid debt expansion, unlimited QE etc are all gas pedals that could trigger such acceleration, as is the rallying and increased adoption of viable alternatives. But policymakers on both sides would rather people believe that some of the most consistently failed policies in economic history could never fail in the US. Straight up ponzi shit.