Yes, it's a low risk. Perfectly executed this is maybe a risk of one in ten million. So on a worldwide scale this means that it would happen every day, to someone.
But it won't be perfectly executed. Let's say you need to do a transaction while you're moving house. And maybe one of your relatives is in financial trouble.
You (probably) don't have the means to do what banks do, and hire an armored transport.
With collaborative custody companies like unchained, this is actually not as difficult to do right as you're making it seem.
Further, unlike an armored truck full of cash, security by obscurity is really easy here. That and for a short duration (say moving houses as you suggest) one could wipe a cold wallet clean and just remember a seed phrase. Personally, I don't have enough wealth to make this sort of maneuver at all worth it, but it's completely do-able.
I was once running a service that had redundant ISPs. None of them had had an outage in years. Then we needed to do a change, the first one ever that required disconnecting one of the ISPs. In the 4h window of our planned job the remaining ISP had its first outage that affected us. We had to apologize to many big name customers that depended on us.
Since then I don't believe in short SPOFs.
You could get hit in the head by a robber on your way moving your furniture, because the robber thinks you may be hauling high value stuff, and lose the passphrase. If you back it up on paper then the unguarded house may be broken into, and they steal the bag that had the paper passphrase.
Extremely unlikely that it'll happen to you, but extremely unlikely things happen all the time to someone.
I feel what you're saying is true, but not really something that should matter in a criticism of BTC when BTC is actually easier to secure than other dilution proof assets like gold.
3/5 multisig with collaborative custody would likely already be at least as safe as dollar checking accounts.
I would also recommend against keeping assets as gold in your basement.
> 3/5 multisig with collaborative custody would likely already be at least as safe as dollar checking accounts.
I think that's off by orders of magnitude. If the whole US did this then I'd expect thousands to screw it up every year.
"Just don't make any mistake, ever" doesn't scale. Not to more people, and not to any one person, given enough time.
It's like running a yellow light (and the occasional red, when you thought it'd be yellow a bit longer). You can go your entire life never being in an accident. But there are accidents every day because people run yellow lights.
But it won't be perfectly executed. Let's say you need to do a transaction while you're moving house. And maybe one of your relatives is in financial trouble.
You (probably) don't have the means to do what banks do, and hire an armored transport.