The startups in that article don't seem to be selling entire properties on the blockchain though - it looks like they're doing things like buying a property and then selling fractional interest in that property to different investors as tokens.

I'll believe that multi-sig wallets solve this when I hear frequent stories about regular human beings (not highly sophisticated tech insiders) who both understand them and use them successfully.

Or, do what enterprises do with sensitive documents: Store it with a custodian (or a hardware wallet).

Mutli-sig wallets are but one non-custodial solution.

Not long ago, Signal demonstrated a way to recover passphrases in a way that server compromise doesn't really reveal anything at all about the passphrase itself: https://signal.org/blog/secure-value-recovery/ The OPAQUE standard also has similar properties to Signal's design but much more cheaper to implement: https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-opaque... I point these out because Novi (Facebook's Diem wallet) implements the latter. These never require keys to ever leave a client device (which inturn could be a hardware wallet).

Useable security will take time. It was a long road from GnuPG to Keybase/Signal. Given the amount of cryptographers and engs building for "web3", I'm sure something useable will crop up. May be it is Moxie himself who comes up with it, who knows? ;)

So two escrow companies and I each have 2-of-3 keys.

At this point what is the blockchain providing that normal title records don't?

It isn't as much about blockchain, than what NFTs enable. Properties can be sold digitally, like any other goods are on e-commerce websites, for example. Of course, NFTs aren't strictly needed, but could be used as a cryptographically secure (for some definition of secure [0]), publicly verifiable, record of ownership.

[0] https://moxie.org/2022/01/07/web3-first-impressions.html