"It's a hard claim to support that Zappa wasn't much of a musician."

No more hard a claim than to say Bob Dylan isn't much of a musician.

Our opinions are not facts, especially when it comes to iconoclast musicians, and I include the Dixie Chicks in the list of iconoclast musicians.

If I love Frank Zappa, but hate John Lennon and the next guy loves Lennon and hates Zappa, who is factually correct when I say Lennon is an excellent musician, and the other person says he is crap?

Let us not forget, very gifted musicians have a tendency to make such claims about one another with a fair amount of frequency, though rarely as a matter of public discussion or debate.

Defining what makes an excellent musician is often a highly subjective matter of opinion.