It is not equally secure, if bank loses you money you have recourse, if bank loses your key (a fire, a flood) it's gone.
Multisig is a pretty common setup for crypto and there is software that makes it easier.
And to think the conversation started with an observation that people can't even remember one password.
A safe deposit box may be affected by other things and if those things happen they don't have to "make it right", if you go to the courts and make your case you may find that they are not at fault and you are not owed any compensation.
There is a long history here of once trusted institutions turning out to be fraudulent.