I like some of the ones listed. I have one many people wouldn't think of.
Richard Marx.
Not only did he do his own stuff but before he was popular he wrote #1s for Kenny Rogers (Crazy), Kenny/Kim Carnes/James Ingram (What About Me), Olivia Newton-John (Best of Me) and a few more. He was also doing backup vocals for Lionel Richie (You Are, Running With the Night, All Night Long) ,Chicago 16 and 17, Whitney Houston's debut (All at Once , Greatest Love of All, Saving All My Love) and a couple Madonna albums.
After he was famous, he wrote tons of stuff, including Vixen (Edge of a Broken Heart), Ann Wilson/Robin Zander (Surrender to Me), N Snyc (This I Promise You), several Keith Urban songs (Better Life, Everybody, Long Hot Summer), plus songs for Barbra Streisand, Vince Gill, Luther Vandross, SheDaisy, Josh Groban, Kenny Loggins, and tons more.
He has written a #1 song in 4 decades. He plays everything.