It's a pretty accurate assessment. A large number of people depend on freemium email addresses provided by the likes of gmail and many others as well as some ISPs. Those are only valid for the duration of your relationship with the companies behind those and that relation may be terminated for reasons beyond your control. Then there are a lot of company email addresses that are only valid for the duration of people's employement. Only a small minority of people have their own domain. And saying that they own it would be a stretch. They merely own the right to pay to renew their lease every year.

Then there is the wide spread practice of tying identity to a single email address that may be used to reset passwords. There is no good technical reason to limit it just one email address or indeed just email addresses; that's just a historical quirk that gets mindlessly copied by world + dog when they spin up a new service because of the mistaken belief widely held by non technical product managers that that just is how things are done. Only a minority of websites provide 2FA, which enhances security but does not solve the root problem of people not owning their identity. Changing your email address is not a feature that is commonly supported either. Whatever email address you pick when you signup is what you are stuck with.

If your email provider shuts you down, you lose the ability to reset passwords, receive notifications, etc.

IMHO the way out of this mess is to start making multi modal signins more common. Some companies already do this but it is not a widespread practice. Simply encourage users the ability to add multiple ways of authenticating themselves. Phone number based authentication, device based authentication (using e.g. QR codes), public key based authentication (ssh or otherwise), social media account based verification, etc. are all viable strategies to authenticate. And why have just one? Combined with 2FA this makes for a much more durable account ownership. It can also remove a lot of onboarding friction as you don't actually need users to provide a lot of information about themselves.

A lot of the reasons for this not being so common has to do with a misguided notion of big trillion dollar companies wanting to "own" the relation with their users. So Google will not allow people to use their MS owned identities to sign in or vice versa. Even though both implement variations of OpenID 2.0 and generally have a large overlap in terms of how they implement security technically. It's a simple matter of ownership. They own you. They consider you their property. Your identity is theirs to control. This is the notion that needs to be challenged for this to ever be resolved.

Imagine that citizenship worked like that. It doesn't of course. But imagine. There would be a lot of stateless citizens no longer able to prove who they are because gmail shut them down or whatever. That would be unacceptable of course. Banks can't get away with that either. A passport is all you need to reclaim ownership of your bank accounts. And in case of your death, a death certificate and some paper work from a notary is good enough for your surviving relatives. Online identity should be just as strong. People confuse the means of authentication with the actual identity.