Oh, I don't agree with that at all. Let's say I give a bass player a chord chart, just the chords. He'll come up with a bass line that works but that's his job. I wrote the music, the song has my name on it and that's it.
Did I "write" that bass line? No. But there wouldn't be a song to put a bass line to if I hadn't written it. And believe me, if I'm not liking what the bass player's doing I'll keep letting him know until I'm happy.
Coming up with a drum part to a song is the same thing. The song exists, it has a melody, lyrics and chords, verse, chorus, all of that, and unless it was a collaborative work then the person who wrote the melody, lyrics and chords deserves sole credit for the song.