Just as firefighters manage forestry through controlled burns shemitta would perform a similar function for the economy by applying what would amount to a controlled business cycle.
To say an economy cannot survive a shemitta is to deny that economies do it all the time, only they call them recessions and depressions. The problem with uncontrolled business cycles is: first, they are seen as unwelcome, so that now we are in an era when we are trying to manage the business cycle out of existence, to the detriment of a healthy economic system, not unlike the unhealthy forests that grew out of the wrong-headed notion that forest fires were bad.
Second, uncontrolled business cycles affect mostly the economic but not the political and spiritual sectors, where they are at least as, if not more important.
Third, uncontrolled business cycles are uncontrolled and unanticipated so they tend to be more harmful than controlled shemitta would be.
Fourth, uncontrolled business cycles do not alter the fundamental social relations between elites and subject populations the way a prescribed shemitta would, and so they do not threaten the status quo of power in the society.
Shemitta functions as a sort of built-in term limits to the entire public social order. Not such a bad idea, on the face of it.