In this respect, Apple got pretty lucky. Most users were not using reduced keyboards in 1987 when they originally decided to add the Control key separate from Command. Plus, Mac OS didn't even have a native terminal at the time; I assume there were terminal emulators for networking/serial use but I can't imagine that was top-of-mind for Apple either.
Regardless, Cmd-C is definitely a more convenient shortcut than Control-Insert, even if you do have the keys for the latter.