I like many song by the Beatles. I think they're overrated, but my impression of their rating by others is absurdly high.

Calling people that think they're overrated "deniers" seems in-line with my general impression that their rating is just too high, possibly for any band. I know you probably didn't mean it totally seriously, but I personally read it as more serious, even if not totally serious, than calling someone an Elvis denier as an example.

It also might stem from the fact that I more often tend to view music in terms of things I like and don't like, rather than good or bad. As a result, any time there is a discussion of the "best" bands of all time (and few such discussions would leave the Beatles out without specific selection criteria), it's hard for me not to consider all of the bands mentioned as overrated by whoever is ranking them.