Shimomura composed some good tracks, but didn't provide nearly as much as the rest. I won't miss her absence, personally. I'm definitely only speaking in terms of volume, not quality versus quantity. Xenoblade's OST is just that good, but she was just so overshadowed, it's almost funny. It's naturally easier to love the others' work more.
Composed and arranged (plus ones composed by them but arranged by someone else):
Yoko Shimomura: 3 tracks + (8*).
ACE+: 29 tracks 
Manami Kiyota: 46 + (4)
Yasunori Misuda: 1
*For 1 of those, it was just a strings credit. ACE+ arranged Minami's 4, and 3 of Shimomura's. 
The star for me in Xenoblade was Manami Kiyota <3. I was so sad to see her (and ACE+) absent from XCX, but I'm glad they're back. Minami's themes are just so damn good. How she can make multiple, beautiful themes like Satorl Marsh (Night), and then do stuff like Zanza's World... ah! I loved her stuff; it stood out more than the others', but the majority of the OST is just amazing. Props to everyone.
Can't wait for this OST! 
If anyone wants to see for themselves (I just counted for break-down purposes).