Operator has very little access. It's kind of a 'demonstration' group created by ULX.
Owner group, if you want high access commands, should inherit superadmin.
Gmod only knows, by default "out of the box" standards, three groups. Superadmin, Admin, and 'default', aka ULX 'user'.
I'll never understand why some other gamemodes and mods made a 'owner' group.
Superadmin is the access Gmod expects for a server 'owner' to have.