Here's Sullivan's analysis:
That’s a straight-up, un-weighted average. On average, when Doumit’s been behind the plate, his team’s allowed 5.37 runs per nine innings. On average, when Doumit hasn’t been behind the plate, his team’s allowed 5.00 runs per nine innings. This does not adjust for playing time or for pitchers caught, so of course it isn’t perfect. There’s a lot of potential error in here. But this could also be capturing everything — throwing arm, pitch-blocking, pitch-framing, game-calling. CRA is a hopelessly flawed statistic, but for whatever it’s worth, it isn’t kind to Ryan Doumit, which goes along with his defensive reputation.
Teams throw about 1,440 innings a season. Over 1,440 innings, a 0.37 RA difference is equal to about 59 runs. If we’re in any way capturing Ryan Doumit’s true defense as a catcher, he’s really not good at it, and his bat probably isn’t good enough to make things much better.