"The financial statement of the economy has to balance." The heart of MMT is that the imbalance between money coming in to a powerful central government and money going out is the primary contributor to growth (or contraction) of the economy as a whole. When it is balanced, the economy is neither growing nor contracting. When the government increases the public debt in a sustainable manner (i.e. people are willing to buy all the Treasury bonds being offered) the economy improves.
"This is merely a backdoor way of transferring assets in a deeply unaccountable way." It's not backdoor and it's not unaccountable; it's tax policy.
Only if our measures of economic strength are fundamentally measuring how much money is in it. If what is important is prudent use of resources then there is scant evidence that that is a good idea. And the reason we have an economy is to work out what 'prudent use of resources' means in practice. Governments have no advantage over private individuals in husbanding resources over the generations (look at how many governments make a pigs ear out of setting up pension, retirement systems and infrastructure spending).
Strategically, MMT theories that I've read seem to say that government is a positive, but if we can't be sure who is paying for it maybe nobody is, so the net impact is probably also positive.
That is clearly crazy, but also looks uncomfortably like an honest take on what a lot of governments do in practice. When the government takes on debt, it isn't obvious who is paying for it - the lender thinks they have an asset, so it isn't them. Identifying which taxpayers will pay the money back is as hard as unwinding who money printing is actually hurting.