Granted, the Wikipedia definition in your link does appear to be based only on fiat currencies.
And your last statement is a fair point, from the point of view of how one might profit from Bitcoin.
But the monetary theory of Bitcoin is not about making profit, it is about creating non-fiat currencies.
And in that, it has had some success, evidenced by the plethora of non-fiat currencies which now exist, using the general principles of distributed ledger it made famous.
The definition of modern monetary theory in Wikipedia looks like a great example of established knowledge ignoring the presence of new knowledge.