Completely? No, banks do a lot more than the retail accounts everyone is familiar with.

Side effects? ATM ownership? Usually the privately owned ones are much more expensive, borderline scams. Credit card processing?

Depending on how liberally you take the intent of the question, I haven’t directly used a traditional bank in decades. However my online bank has more capabilities than my credit union. And who would put investments in a bank when there are so many better investment options? My mortgage was started with a bank but sold to a loan processing company: if I had gotten it through my credit union, they don’t sell mortgages. I suppose car loans are typically a Main stream bank: my credit union offers port terms for those, can’t compete