You own a legal claim to the deposits you made with your bank. [...] You might be able to cause a spend. [...] There is no counterparty that has guaranteed this to you.
Actually, deposits under $200K (IIRC) in US banks are insured, so you can say that there is a 3rd party who guarantees that your money are safe. There is no such guarantee with BTC, and no recourse if your Bitcoins are stolen (that had happened already.) This alone makes banks valuable: they, at no cost to you, insure your spending.
There are various situations in which you would not even be able to enter a spend. One example is: local network or electrical outage.
Those are basically acts of God; they are so rare that nobody in the modern society is worried about them. When was the last time you couldn't withdraw money because of local power outage? This may be a problem after SHTF, but everything will be a problem at that time. The Bitcoin does not fare any better, actually, because the bank may have a diesel generator; but what percentage of Bitcoin network is independent from the grid? That includes communication lines, of course. If anything, I'd expect banks to recover far faster than the BTC because individuals will have far more serious needs on their hands than to be a BTC node.
The fact is; while you control the private keys, you don't control the bitcoins.
May I have an example when I, an owner of a BTC wallet, know the password but cannot control the bitcoins? (Outside of a SHTF scenario, of course.) It is true that a 50% attack is a possibility... but a very remote one. Once someone gains control over the decisive portion of the network, BTC will be effectively dead. You can have far more concern about the crash of conventional currencies - especially because such crashes periodically occur all over the world (like every few years.) Those are not scenarios that play out in normal operation of the currency (like loans, payments and transfers.) We should focus first on how the currency in question operates in peace time. Only after that we can look at how it reacts to unusual events. (Most of currencies fail right away, with exception of precious metals, such as lead, brass, silver and gold.)
Note that "control" does not have to include everything under the Sun. You may own your car, but it's stuck in the snow and you cannot drive it. Does that mean that you don't own it anymore? If someone steals your car from that snow bank and drives away, he is now in control, though he has no right to be in control. You are now only legally an owner; but as matter of fact the thief owns the car because he can do anything he wants with it, and you cannot. If you control the wallet with BTC, you control those Bitcoins as well (unless the wallet has a mind on its own, which is fairly rare these days.)
Just a toy currency that is part of a virtual game environment.
Ah, but that's not for you or me to decide. It's for the GOVERNMENT to decide - and it has decided that BTC is money. Period. They have authority over such matters.