You’re really close:

2-of-3 collaborative custody multisig where the “bank” holds 1 of 3 is the solution here. Unchained Capital’s goal is to provide this solution, and they’re already doing it.

If a bank tried to do 1-of-2 or 2-of-2, Unchained’s model makes that instantly obsolete. It’s honestly genius. It’s bank level security for a back up, but they don’t actually control your funds.