There’s a secret behind the last three decades of pop music: Writer-producers run the show. This is partially a numbers game — Whitney Houston had an inimitable voice, but Babyface had a hand in over 200 R&B hits, so who exerted more influence over the direction of a genre? When it turns out that, like Babyface, gifted writer-producers can also sing well, that only helps their cause.

Enter Ty Dolla $ign, a triple-threat capable of writing for stars (see Rihanna’s “FourFiveSeconds”), jumpstarting singles with guest appearances (Fifth Harmony’s...