Between the four Donny Cates cosmic OSHCs, the Thanos one is the completely redundant one. All of the Thanos OSHC material is in both the Marvel Cosmic Universe OSHC and the Cosmic Ghost Rider Omnibus. If you wanted Cates' Inhumans and Silver Surfer: Black, you could upgrade to the Marvel Cosmic Universe OSHC since you're not interested in the other Cosmic Ghost Rider stories in the Cosmic Ghost Rider Omnibus.