Why not ? Consider two scenarios which will lead to the end of banking system.
1- If everyone start using crypto and no one used fiat, then there will be no need of banks. (this is an ideal scenario which is less likely to happen anytime soon)
2- If people start keeping wealth in bitcoin and less money in banks. Banks uses the people money in investments and this keep the circle of the bank running. If banks are short of fiat, this will bring their operation to halt. (a more likely scenario to happen soon)
A better way to look at it with Bitcoin, it would significantly decrease our reliance of banks, but not necessarily that Bitcoin would replace banks. There's a significant difference between both statements. Because truth be told, banks still have their own use-cases for loans and such.
I agree with you. While cryptos do make banks unnecessary, they can still be useful and very important for many people and for some specific purposes. For instance, some people just don't feel comfortable being responsible for keeping their funds safe. They want the banks to be responsible and to store the money for them. So cryptos are not going to be attractive for such people, and even if cryptos go mainstream, these people would probably want crypto banks to manage and store their cryptos as well. Apart from storing, there's also this feeling of legitimacy which having money on a bank account does, and having cryptos or just storing cash under the bed to not.