In this video, he's basically pointing out that you need all three private keys to reconstruct the xpubs, which are needed to prove spending authority... Which he implies defeats the purpose of multisig for individuals.

"Multisig does not create a 2-of-3 redundancy - it requires 3-of-3 redundancy to create 2-of-3 spending authority, and that is very dangerous if you decide to use it for yourself. Because, for yourself, you don't need 2-of-3 spending authority, what you need also is 2-of-3 redundancy, and if you don't have that because if you lose a single seed, you lose all of your money."

This is where this reasoning is incorrect:

If you're thinking you need to reconstruct xpubs, you're thinking about private/public keys the wrong way in this context. There is no reason to be in a situation where you have to reconstruct xpubs.

You can think of xpubs as the wallet's public spending key. xpubs specify what wallet you're spending from. It's the original public key constructed from the original private keys. Yes - you need that to spend. If you lose that, you can't specify what wallet you're trying to spend from. It's the "from" address - you can't send without the "from" address.

BUT - knowing the xpubs doesn't actually give you spending authority. You can't spend with it.

That's incredibly important. Why? Because you don't have to treat your xpubs like a private key! The stakes aren't that high - you can store your xpubs digitally in multiple locations. You can have backups upon backups.

With a private key, too many backups means increased theft potential. That's not the case with xpubs. You should never be in a situation where you have to reconstruct your xpubs in the first place!

So the idea that "you need all three private keys to reconstruct your xpubs to send" is a completely moot point.

Just like any wallet setup, it's dangerous if you don't understand it. As long as you know to store multiple xpubs backups, 2-of-3 multisig is significantly less dangerous than single sig + passphrase.

If that's too complicated for someone to understand, third party collaborative custody solutions like unchained fix that. During their vault setup, they tell you to store a digital copy of your xpubs, and they hold a copy themselves. Unchained would have to completely die AND you'd have to lose access to your cloud or PWM for you to lose access to your bitcoin.