Original sentence: Cliff claims he is "the most radical rock star there has ever been".It is true that his protracted chart success invalidates radio stations' claims that he does not enjoy public support (or, at least, not from their target audience)
Edited sentence: While it is true that his protracted chart success invalidates radio stations' claims that he does not enjoy public support (or, at least, not from their target audience), it is difficult to accept his claim in the same documentary that he is "the most radical rock star there has ever been"