I'd be surprised if Google doesn't already enforce TLS for other big peers like Microsoft. In your universe, what do we need a broken standard for?
> you require the radical centralization of all cryptographic trust on the Internet into a tree-shaped PKI
Web PKI isn't radically centralized? It's worse than radically centralized, because you can break Web PKI by attacking the weakest CA.
> it drives a stake through the heart of the last truly motivating problem that DNSSEC was going to solve.
MTA-STS may give people cover to pretend they don't need DNSSEC. But make no mistake: it doesn't actually solve the problem.
It's interesting that technical opinions of DNSSEC have devolved into such irrational hatred that people will openly proclaim that fake security is better than actual, DNSSEC-provided security. Yes, DNSSEC is complex. Yes, it has issues with network privacy. But those arguments don't redeem MTA-STS, which is fundamentally broken.
Why should anyone be discriminated against based on the size of their mail server?
On the other hand: I believe email is a technological dead end, and that we are not evolving towards an Internet with a more distributed email system, but with less distribution. I think that, from a utilitarian perspective, the only mail servers that matter are the ones that Google and its peers run, and that's the threat model I care about.
In my threat model, MTA-STS basically eliminates the concern DNSSEC/DANE addresses. Since your threat model includes rarely-used independently-operated servers (note that mine includes things like Fastmail and Proton!), servers that won't have cached assertions, MTA-STS is inadequate for your needs.
The problem I have with your argument is that to fix your problem, which is an extreme niche, you require the radical centralization of all cryptographic trust on the Internet into a tree-shaped PKI whose roots and trunks are controlled by world governments and whose technical underpinnings date back to the 1990s. Even if I was to stipulate that you had a point, DNSSEC wouldn't be a viable answer to it.
But that's a normative argument, and my point about DNSSEC being done is positive, not normative: deployment of MTA-STS is going to end DNSSEC. Not because I want it to (though I do) or because it should (though it should) but because it will: it drives a stake through the heart of the last truly motivating problem that DNSSEC was going to solve.