I don't get the argument. Is the author complaining about complexity of languages like Rust? I.e. only simple languages supposedly have longevity? C++ is complex, yet it already exists for quite a long time too.

Just because C happens to be a long used language doesn't mean you shouldn't be using newer and better languages and that those languages can't be used for a long time too.

C is used not due to big benefits, but mostly for legacy reasons today. Basically a lot of projects are already stuck with it. But for new ones, surely use Rust, not C.