I think that's just the significant difference between fiat and bitcoin fiat can fall in value for a long duration while the dip in the price of bitcoin does not last long, it can only last for some couple of days for example (3 to 4 days) sometimes it might not even get to this before it will start appreciating again. While the dip in fiat can last for some couple of months sometimes years before it will start appreciating again, so therefore I think is not a bad idea if the bank choose to hold bitcoin as reserve.
Which is why bitcoin is literally the most perfect thing for banks. Because they do not even have to give interest to people to keep their coins there, and if they do, it would be very small.
That means, they can loan out, and make a lot more. But that's how the trouble starts, because the world is in debt because of this.
Let's say I give 100 dollars to banks, and they promise to give me 110 back next year, that's savings and that's how they get their money right? So, what should they do? They should loan that to someone else and ask 120 back in a year, correct? Ten per month. Instead, they give that to 9 different people, same money.
Then they get 1080 back, out of my 100, pay me 110 back, and the other 970 is their profit. There are many banks and so forth that leverage this way.