While you're right that Perkins' discrepancy is somewhat larger than one might expect, the stats that you choose to back up that assertion are misplaced I think. We're talking about the difference in strikeout rate for a single player, not all starters vs. all relievers. This is a bad comp for a large number of reasons, not least among which is the fact that, on average, starters are simply better pitchers. A way better comp (albeit a much harder one) would be pitchers who did significant time in the majors as both starters and relievers. I know that it's not terribly uncommon for failed starters to become lights-out relievers, and even closers. What reason do we have to disbelieve in Perkins' K numbers as a reliever? After multiple full seasons in the role, the sample size isn't exactly miniscule.