It doesn't matter. In France, there are 70 millions people. Remove old and young ones, and the ones that are not clients in your bank. Then spread the usage on the week, then on 24h, divide by the number of requests that actually hit your Python backend (so no cache, no static files, etc). You got what ? 1000 requests/s top ? That's nothing.

Bank sites are not youtube.

Besides, operations on your bank account don't even hit the Python backend, but a dedicated system. Usually some COBOL dinosaure they froze, wrapped into a Java service and exposed through a RESTish API so that the rest of their system can use it without ever having to touch it again.