When more currency X is issued, the losers are people (including lenders) who are locked into assets denominated in X, if this leads to a devaluation of X relative to other things.
The status of fiat being legal tender for all debts is what makes lenders unable to demand other currencies but they can execute forward contracts of X versus a basket of commodities for example.
It seems to me that’s kind of half-a-loaf MMT. Or, to borrow from The Matrix trilogy, it's the spoon-bending level.
Where the full loaf (“there is no spoon”) is: Government is not constrained to take on debt at all to finance an excess of spending the over revenue. The idea that, if the State chooses to create net new tokens in the economy (remember, the key points of MMT is that fiat money is created by the issuing government spending and destroyed by the issuing government recovering it), it must seek the permission of someone with a surplus of existing tokens willing to sacrifice them for a greater number of future tokens, after which the government's pet (but “independent”) token-issuing body will see to the issuance of additional tokens is kind of bonkers, but that seems to be how MMT would view the current relation between fiscal and monetary policy.