Actually, I think that your figuring is off the mark. First of all, if you assume the results for 7th, 8th, and 9th are independent, the number is closer to 34% of the time than 35%. Second, those outcomes aren't independent--big innings are more likely to be followed by big innings than would be expected by random, so it would be less frequent than that. Third, if my pen is giving up 2 or more runs per 3 innings in less than (probably) 30% of the games, that's really not bad. Let's say 30% of 8 ERA and 70% of 2 ERA equals a total ERA of 3.8, which I would certainly take.