I do wonder what the legal basis for copyrightability is here; to some extent, this sounds like the publishing companies might be making legal arguments up that

I do wonder what the legal basis for copyrightability is here; to some extent, this sounds like the publishing companies might be making legal arguments up that would not stand up in court. Song melodies are copyrightable, as are recordings, and lyrics. But chord progressions are not. So a guitar tab containing only chords (not lead melodies) and no guide lyrics sounds to me like it ought to be entirely fair to publish. Of course, many tabs include lyrics or other elements that verge into copyright infringement, but the idea that all tabs are necessarily derivative from the original song and subject to its copyright sounds wrong on the face of it.