It's not that mathematical models make a theory more valid or sophisticated. They make it testable, which is why neoclassical economics > both Austrian and MMT.
If Austrian school economists want to gain mindshare, they should develop models, backtest them, and report the results. Same for MMT.
By the way MMT is a political phenomenon. There are very few professional economists who think it is workable.
Not everything is testable. That’s a modern reductionist approach to reality. Scientifically oriented people tend to think the opposite because scientists are strongly biased towards studying testable phenomena, providing a false impression of general testability.
If Austrian school economists want to gain mindshare, they should develop models, backtest them, and report the results. Same for MMT.
By the way MMT is a political phenomenon. There are very few professional economists who think it is workable.