[tremon]

I'm not sure what point you're trying to make, but:

  $ sudo /bin/sh -c su -

It's never useful to deny certain commands to a user if that user is allowed to open a shell. Any shell. So you probably want to change that first line to

  (ALL : ALL) NOEXEC: ALL

and provide a whitelist for all tools that do spawn children as part of their normal operation (such as apt, dpkg, and probably half of all unix tooling).

[yrro]

It's how I've trained myself to avoid 'sudo su -' - by removing my user's ability to use sudo to run su ;)