Your reasons are not valid or rational, sorry. Insurance companies cover whatever you get a policy for. If you have something of great financial value, then you get a written professional appraisal and get coverage from the insurance company. You don’t put things in a safe deposit box instead of getting insurance coverage. Expecting the bank to provide this coverage is like expecting a parking lot to pay if your car is stolen.
As I said, you take the higher priced coins from the collection and put them in a safe deposit box. Having a locked box in your house for highly valuable items isn’t as secure, because you could be away on vacation or even at work that day giving plenty of time for thieves to steal them. The safe deposit boxes at banks are highly secured with alarm systems and during opening hours there are guards. You couldn’t possibly offer that protection from a locked box in your home. I get a safe deposit box at no cost from the bank. The costs for an additional one is also cheap.
I know many stamp and coin collectors and they insure the higher priced items and store them in a safe deposit box. Yes, a plane could crash into a bank, but it could crash into your house too.