Not disagreeing with your logic, but interpreting things a little differently...
I think, between Fred and CJ, highly likely that one or both will be injured this season. Whaley has gone out of his way this offseason to surround EJ with talent on the O-line, in the WR corp, and in the backfield. CJ's value is playoffs or bust mentality at OBD, not in a player to be named, or in resigning him to an extension. Front office is playing this season for their jobs with new ownership looming, regardless of what they say in the media... either that or they are really naive. 4 quality backs are insurance for this, IMO. Marrone may not use more than 2 per game, but he almost assuredly will use more than 2 in a season. Whether CJ signs an extension or not is irrelevant to the current regime if they're not here. And if they make the playoffs and he doesn't resign, it's not the end of the world.