I'm not sure it is. That set up involves a lot of trust in a third party (the bank), which I would not be comfortable giving them. Are you absolutely sure no one at the bank will ever take a peek at the piece of paper you give them to store? Even if you go in to their vault yourself and lock it in a safe deposit box yourself, you have absolutely no way of knowing that they don't have another key which can open your box. You are placing complete trust in their security set up and their staff.

If you are going to trust a third party to hold your seed for you, be it a bank, a lawyer, a friend, whomever, then it would be a wise move to encrypt it first.