Like many other configurations, the system configuration is now in /usr/etc/sudoers (usr because it’s from the system - don’t ask) and /usr/etc/sudoers.d/.
A file in /etc/sudoers.d or /etc/sudoers will override values from /usr/etc.
If that sounds more complicated, that’s because it is. 
But it’s also much more flexible.
A fresh installation won’t improve anything; you’ll be right back where you are right now. Some things have simply changed (don’t they always).