I agree with everything you've said, except the conclusion: C can't add proper safe RAII, but being "proper and safe" is not a threshold C even tries to uphold.
But would a destructor that runs automagically when a value goes out of scope, even if it's not properly initialized (and with zero regards for copies or moves) be in any way better than a defer that's explicitly called after it is initialized?
Hell, since RAII is an opt-in type-level infectious (in the sense that if you have an RAII member in a struct the struct is RAII) mechanism you can require that RAII structs be initialised.
Given the compiler would already need to know that a local is of an RAII type in order to insert the drop, move, and copy glues it’s not exactly a big requirement.
Whereas it's perfectly possible to only defer a statement when you know the "object" has been properly initialized.
That's why defer makes sense in a language like C (even Go), but RAII does not.