And my mx also needs to be backwards compatible to exchange email with older systems out there on the internet that speak no TLS at all.
I don't dispute the merits of tls1.3 in any way, or that it functions as designed.
Aside from email, the entire centrally hierarchical root CA system is a hack job. Why does your browser trust certificate authorities from turkey and mainland China?
CA cert issuance transparency and public logs are a further hack job piled on top.
My point wasn't that magically the existence of TLS 1.3 makes email secure but that TLS 1.3 is "a hack job piled on top of a hack job" too and it's fine.
However, since we're here now: Depending on which browser you use there are two potential answers to your question.
In Firefox the answer is always that Mozilla decided that the CAs which are members of its root trust programme met its requirements. Mozilla's oversight of the Web PKI happens entirely in public. If you have a specific reason to think there's a problem at a CA based in Turkey or Mainland China which is a member of that programme you should raise it.
Otherwise, this decision was made by your OS vendor. If you use a Free Unix then in effect that's still Mozilla since all the popular Free Unix system implicitly or explicitly delegate this to Mozilla, but if it's Google, Apple or Microsoft then that's a matter for them, and they do not have public oversight, good luck with that.
Now, since you mentioned Turkey and Mainland China specifically that would narrow things down a lot (unless you run Windows). Mozilla only trusts Kamu (the Turkish government CA) for Turkish stuff, so, it's unclear what sort of threat you imagine they impose. When I say "Turkish stuff" I mean like the Turkish government's sites, its military, schools that sort of thing, not say a Reddit about Turkey. TURKTRUST which you might have heard of is not trusted at all.
When it comes to the Chinese mainland (as opposed to Hong Kong or Taiwan) there are several more, including GDCA and CFCA but we don't have any particular reason to doubt these authorities behave in accordance with policy. They seem to be exactly what you'd expect, for example CFCA is a financial outfit, and sure enough it issues certificates to various Chinese banks. Would it be a good idea for a foreign critic of China to keep money in those banks? Perhaps not, but that's hardly a problem with the CA.
This weekend Rescorla et al published the Internet Draft of Compact TLS. cTLS is (intended to be) exactly the same functionally as TLS 1.3. Except that the "spelling" is er, compact.
For example, your "real" TLS 1.3 connections have a connection ID in them. That seems sane right? Well, the content of that ID is a bunch of random gibberish, echoed back by the server. It doesn't do anything useful at all, it isn't identifying anything, it's just some random bytes in a system that already has dozens of random bytes that are there on purpose anyway. So why is it there? It's there because in TLS 1.2 that connection ID field was used to resume previous sessions and so lots of middleboxes will just assume everything must be fine so long as you fill out the connection ID and then the remote server appears to continue the same session. Such middleboxes can't snoop because they don't know enough about this hypothetical session which never happened, but since they are just security theatre anyway it doesn't matter, your connection succeeds. This makes TLS 1.3 actually work, developing such workarounds by tweaking the "spelling" took about a year.
But the security proofs are the same for compact TLS and the "real" TLS 1.3 shipped in your browser. It's just that the real thing is "a hack job piled on top of a hack job" because that works.
Mathematics doesn't care how you spell it, if you've come up with an incredibly convoluted way to do something apparently easy, but the math checks out anyway, it still works.