No, Sommers will come back in the next 3 chapters.
Sommers IS much slower than Ray, but:
The God's Knights have the Super Ducks they ride, which let Garling catch up to Rocks.
If Sommers gets one of the Ducks, he can catch up.
Also a chance Gunko is ordered to go after Shakky. Gunko's weirdly absent here: I could see here protecting the CDs, then coming to fight once they're safe on their ships.
Could see Gunko going after Iris, too.
But, yeah, Scopper Gyaban and Saint Sommers are 100% at least clashing here.