In my amateur economist models, I adjudicate over-saving as a symptom not the disease. It is clear that money issuing does not have a neutral effect (not the same as private firms investing, or private firms being taxed to fund a government project). In the end it comes back to the utilitarian-keynesian view that the government will be more efficient spending that money, or that such a thing would not have long-term effects on the exchange rate, savings, etc.
In my amateur economist models, I explore economic systems with modified electrical engineering diagrams. Money as we define it and subsequently many forms of savings/over-saving are nearly as useless as Instantaneous Voltage (in Joules) or ultimately as abstractly uninteresting as Ground in a working system. It is current flows and movement that are actually interesting/useful, and the not very well defined equivalents for money to its first and second derivative metrics (electricity's Amperes and Coloumbs, for instance).
I have no idea how many proponents of MMT find interest in such similar engineering-oriented views of economics, but general economic theories of inflation/deflation from that point of view seem so primitively useless versus what we know of, say, electric resistance, inductance, capacitance, conductivity, etc.
I cannot tell you if my armchair theories are any better in the long term than the status quo or your preferred models, but only that MMT at least seems to be one of the few areas of economic study currently attempting to address them (albeit indirectly in many cases). That is also not necessarily proof that MMT is correct, just as my models don't ipso facto disprove status quo "wisdom".
