> A struct won't be recognized by the language in order to automatically insert array bounds checks.

If you want automatic bounds checks, then C is not the language for you.

> This is a huge issue.

Could you give an example where it's a huge problem? I'm probably limited by my experience. All of the codebases I've worked on used a single string library. When passing externally/to other libraries, boring C interfaces were used, then those libraries do what they wish from there. The string libraries I've used were mostly, deep down, just structs, with a length member, char pointer member, and encoding stuffs. Passing to the other library almost always ended up just being those member values being passed as arguments to a function, which were copied to the nearly identical structs of the other string library.