It's also not at all a given that website owners would prefer the national CAs -- as an obvious example, most Rust projects (foo.rs) would probably not trust the Serbian CAs as much as they would LetsEncrypt. Even for website owners that live in the country, it seems possible that Chinese website owners might prefer to use non-Chinese CAs. And again, if the solution is to just special-case one American legal entity then we have just moved back to the original VeriSign-signs-everything model.
The real issue is that the CA model has been obviously broken since at least the days of the Comodo hack -- the trust decision for who can certify the website identity is made by the website owner but really clients are the ones that actually care (it's their data at the end of the day) and they have no input. Moxie had a proposal in 2011 to fix this by letting clients decide the policies for how a certificate should be trusted[1] and I think it is a far more workable solution than the alternatives. If one of the LetsEncrypt intermediates was compromised none of the alternative proposals would have any real hope of providing a workable mitigation.