Protestant hymns used to be forbidden, but are now allowed. A lot of them, like Wesley’s “Hark the Herald Angels Sing”, contain nothing unorthodox and are musically worthy. There are some more difficult ones, such as “The Battle Hymn of the Republic”, which is again technically very good, but was written to celebrate the Union armies.
Christian rock is a slightly different matter. The problem is that rock music, bluntly, has the beat of sexual intercourse. So it is very difficult to produce uncontroversially orthodox Christian rock music. Hence most of it is a failure. However I would hesitate to say that it is inherently impossible to produce artistically worthy Christian rock music.
Truth is beauty and beauty is truth, so ultimately it is not possible to produce a good hymn that is a lie, nor an orthodox one that is ugly. However the relationship isn’t perfectly simple. Julia Ward Howe’s belief that God was on the side of the Union armies was hopelessly naive, but the Church Militant is a very real organisation, and slavery was a social evil. If she was completely wrong, the hymn would have no power or interest.
Glad you like the books.