It requires the attacker to be able to type a few characters into a logged in session. If the session is not an administrative one, it's not fair to say all bets were off.

If I give you a Mac logged in with an unprivileged account and you can use only the keyboard and mouse to gain root access, the security has failed.

I think you've conflated this with the attacker having (full) physical access to the machine, which conventionally means access to its ports and perhaps a screwdriver. This is not that.