That is not a myth, it is a fact. The fact that financial crises come at such a cost is now even something of a platitude. In other words, it is an insight that is basically of no particular value, since everyone knows it anyway.
But, unfortunately, it is still something that people dismiss from their minds too often when fiscal policy and regulatory decisions are under discussion. Just think of the global financial crisis of 2008. The costs of that crisis were simply enormous.