The RXI had 2 purposes :
1- Long range reconnaissance
2- Long range escort
And approximatly the same number of missions were performed in both roles.
Indeed, with the Caudron R4 and the Letord Family (let alone the Salmson Moineau), the French developed a concept for escorting recon planes (Farman F40 / Caudron G4 ...) with heavy "fighters".
With the Letord (1917), the planes became "dual role" as they could carry the necessary material for long range reconnaissance (and artillery spotting too), as it was found that for close escort, having two planes of the same type was better.
The purpose of those planes was not exaclty air superiority in the sens that it did not maneuver agressivly, they had to be a "wall" between the ennemy fighters and the planes they were protecting.
Contrary to some saying, the plane was heavily employed and losses were significant.
They often resorted on the help of Spad 13 for those missions : very often, the escorting R11 "bought time" for the Spad to arrive.