I didn't say for the standard account to use sudo; I said for it to use su to switch to an admin account, and then use sudo from the admin account -- as a point

I didn't say for the standard account to use sudo; I said for it to use su to switch to an admin account, and then use sudo from the admin account -- as a point of illustration that if you have the admin password, it's game over, whether or not you're currently signed in as an admin or an unprivileged user. Unless standard accounts don't have access to "su" at all, but I can't see that being the case without locking off access to terminal functions altogether, which would make macOS completely unusable for I would wager most of the people on this site. Looking at /usr/bin/, su is 0755 permissions. Even if you didn't know the username of the admin account, /etc/passwd is 0644 so you could look it up as an unprivileged user -- again, unless macOS has some system level thing blocking all access to the terminal.