The client is perfectly able to verify that when connecting without a central authority by querying a well-known DNS entry. Literally do what the CA does to check but JIT.
This does leave you vulnerable to a malicious DNS server but this isn't an impossible hurdle without re-inventing CAs. With major companies rolling out DoH all you care about is that your DNS server isn't lying to you. With nothing other than dnsmasq you can be your own trusted authority no 3rd party required.
The essence of TOFU is that each party initiating a connection individually makes a trust decision, and these decisions are not delegated/federated out. PKI does delegate that decision to CAs, and them using an automated process does not make the entire system TOFU.
Yes, clients could be doing all kinds of different things such as DANE and DNSSEC, SSH-like TOFU etc., but they aren't, and the purpose of a system is what it does (or, in this case, doesn't).
Yes, that's the entire scope of the web PKI, and with the exception of EV certificates it never was anything else.
> it's pretty clear that with ACME and DNS challenges we don't need a huge centralized system to do this much weaker thing
Agreed – what we are doing today is primarily a result of the historical evolution of the system.
"Why don't we just trust the DNS/domain registry system outright if we effectively defer most trust decisions to it anyway" is a valid question to ask, with some good counterpoints (one being that the PKI + CT make every single compromise globally visible, while DANE does not, at least not without further extensions).
My objection is purely on terminology: Neither the current web PKI nor any hypothetical DANE-based future would be TOFU. Both delegate trust to some more or less centralized entity.
That's not to say that domain typo attacks aren't a real problem, but memorizing an Onion link is entirely impossible. Domains exploiting typos or using registered/trademarked business names can also often be seized through legal means.
Or maybe we return to using bookmarks? Not sure exactly.
It's a web-of-trust and/or TOFU model if you look at it closely. These have different tradeoffs from the PKI, but don't somehow magically solve the hard problems of trusted key discovery.