A very high percentage of the music we listen to and post about is, objectively, simple minded. Bands shouldn't take that kind of criticism as anything except true. Plenty of fantastic bands have written exceptionally simple songs. Um, and yeah, as humans with ears we have "the right" to say just about whatever we want ... bands have the right to create, there's no right that the creation is universally praised.
Some of my favorite songs ever made are "simple minded" ...
... I don't see that being all that negative of a phrase.
When you say simple-minded, what do you mean? The opposite of 'complicated'? If so, I get that, but the phrase 'simple-minded' just sounds pejorative. Like you mean mentally deficient :p.