No, this is way off.
MMT doesn't model fiscal policy as unconstrained in real terms, only nominal terms. And given the legal authority, of course a sovereign issuer is always able to spend. In this case spending is merely typing digits into a computer. This fact doesn't imply deficits/debt "aren't relevant", but rather deficits/debt work very differently for the currency issuer as opposed to the currency user.
[0] https://en.wikipedia.org/wiki/Modern_Monetary_Theory