Also without a central bank able to print infinite amounts of money and be the lender of last resort many of those banks will fail and when they fail depositors will lose everything. This will further reduce the real return. Net change in purchasing power = interest - inflation - losses.
You could just enter "free banking era" in your favorite search engine and look for yourself. Not all banks failed and not all of them inflated their "dollars". As far as I remember, only one third of them went bankrupt...
Wow only 1/3 went bankrupt and depositors lost everything. I am sure people will be flocking to put their money into Bitcoin banks which have a 1/3rd chance of failing.