OF at catcher are worse than C at OF because:

1) The game may not adequately adjust throwing ratings so that OF may be unusually adept at throwing out runners while a C at OF will be degraded by the game.

2) Mike Bravard has specifically posted that OF are not to be played as C. ie It is against the rules of PB to play an OF at C. It is NOT against the rules to play a C at OF, but it is not advisable as he will be prone to errors and allowing base hits.

At least that is my understanding. I know there was supposed to be a correction of the game to stop the OF'ers from playing exceptionally well at C; but I'm not sure it ever went into effect.