I think Rex is a problem, because he doesn't really fit the system we've used over the past four games. But 1) he's
18th in TQBR through four weeks, which isn't horrible, and 2) it would be fallacious to think that John Beck could step in and replace that production.
The idea that Beck can step in for Rex with no offensive dropoff is so obviously illogical that I don't know we we can debate that argument on its merits.
With that said, this team SHOULD look to add a vet QB that better fits its system. And I would consider offering late round draft pick compensation because the team is 3-1 and the NFC East is so obviously wide open and the Redskins clearly have something going.
If you're going to eventually replace Grossman, swallow the pride now and go out and get David Garrard, Matt Leinart, Matt Flynn, etc before the trade deadline. And then let them get practice reps behind Grossman so long as playing him is a reasonable option. Then if the team falls to .500, pull the trigger.