Greyhound range and the Osprey's additional missions

Does the C-2 Greyhound have longer range than the Osprey?

Yes, in this comparison. The Osprey can land on amphibious ships, but supplying those additional destinations creates more demand on the fleet.

The Greyhound is credited with longer range than the Osprey. The comparison then turns to the Osprey's ability to land on amphibious assault ships as well as carriers. Supplying those ships adds work beyond the carrier delivery mission. Aircraft assigned to that extra work would no longer be available for their original delivery tasks. Taking advantage of broader landing access would therefore require more aircraft.