User blog comment:Argorrath/Gearbox declines Activision's offer to develop a game of Call of Duty/@comment-79.97.217.74-20130113142139/@comment-1263839-20130113181253

Raven Software didn't do any of the balancing, perks, standard maps and spawns etc.

The only thing RSoftware did was create new maps, which suffered because of the damn spawn system, weapon imbalance etc. that Infinity Ward and Sledgehammer created.