I was told Linux Mint is ... not that great for a variety of reasons, none of which I understood.
I was told to use Ubuntu MATE, which is what I use now.
What were the reasons you were given?
My guess would be from the backend perspective of the type of person who would actually get into the OS.
For most people coming over from the Windows experience, the Mint Cinnamon distro is going to be the most seamless experience with plenty of support and community involvement for typical challenges.
Since MATE is just the desktop environment it runs Ubuntu underneath the hood, which means it has Canonical's support behind it.
Mint uses Ubuntu's repositories.
It's really 6 of one and half a dozen of the other for the average user.