quite simply, if many people who begin to know the benefits of storing their assets in cryptocurrency can be safer, can be more profitable and can be saved without a monthly tax, it will make the bank afraid of losing its customers.
Broadly speaking, what you say is true, but it all depends on the government and all the currency developments are dependent on the legality and the investors themselves become banks and crypto currencies in the hands of the government.
Such scenario is a long long way down the road. And I don't see it in our horizon yet. The existence of banks will still be here as long as many of the problems dealing with crypto is not yet fully addressed. Crypto is a very high risk investment. Though it resolves issues of speed of transaction and fees involved, yet, we are not ready to embrace it fully in our daily living. The traditional banking system will not be phased out anytime soon.