Don't think there is as big of a difference as we think
At their best it was close. Moss was stuck with Daunte Culpepper in Minnesota and left for dead in Oakland, then spent one year with Brady and one year with Cassel before being effectively finished at age 31. Though he had better teammates and their careers overlapped, the environment Rice was in during the 80s was different from the passing environment this century. From 1998 through 2008, teams Moss was on averaged 540 pass attempts per year. During the years Rice had Montana and Young throwing to him, the 49ers averaged 538 attempts per year. (Yet Rice averaged 13 more receptions and 200 more yards). Rice then went on to have more good season with Jeff Garcia and Rich Gannon throwing to him, making the Pro Bowl at age 40. When two players have peaks that are near equal, the one who played in 100 more games is unquestionably better