One I can say is that there is no perfect system. There will always be bull market and bear market. Maybe you can say this things because Bitcoin and the whole cryptocurrency market is in bull spree at the moment.

But in reality, a whole economy will surely crash more or even deteriorate over time without banks especially central bank. Central bank act as regulator in the fiat system of the whole country. Some countries central banks are shit that seems like they do not know what to do especially when printing money which devalues their fiat value but let us not generalize every bank. Banks were there for decades and does not perform very good all the time. There are ups and downs too. Even the cryptocurrency as a whole has its lapses too.