No, you're judging a book by it's content, but you're missing the point with ERA. You still gave up those runs, you're not an effective pitcher when you're giving up 4 runs all the time, regardless of how weak the hits you give up are. RBI isn't anything like using ERA, because you just need to be the 3/4 hitter in a good lineup and you'll clean up, especially if you're a power hitter.
I personally think sabermetrics are the best thing out there, but think about it. Does your FIP or BABIP matter if you finish the season with a 4.5 ERA? Is that what you're going to use at the end of the year if he's struggled all year?
I think those are better used as an indicator that he's going to turn it around, rather than he's pitched well this year. In the end, scorecards don't go.by sabermetrics, and they shouldn't.