It's by no means an obvious decision or an easy one, but in my opinion, it's the right one.
Parra's line last night was 7 IP, 2 hits, 7 strikeouts, and 2 walks. He has made four starts at AAA, and this is the first one that could really be considered a really nice outing. If you're operating from the viewpoint that Parra needs to "earn his way back" into the starting rotation, then I could understand wanting to let him make a few more starts to make sure he's going to be a good major league pitcher.
That's not the viewpoint I'm seeing it from, and I don't think Parra should really have to prove his way back, especially when the alternatives look bad even to the bad Manny we had earlier this year. If Manny comes back and pitches the same way he did in the bigs earlier this year, he should be expected to put up something between a 4.75 and 5.25 ERA. And that's pretty much the worst end of the range we could expect from him. Given everything we know right now about pitching, even if he continues to walk 5.71 batters per 9 innings and continues his pace of strikeouts, homers allowed, and suppression of hard batted balls, we can expect something around or even lower than a 5 ERA.
That's assuming nothing changes. Maybe he's been working on something mechanically and it clicked last night. Maybe he's just getting comfortable again. I have no idea, and that's the upside of Parra right now. If he did find that control again, we're back in business with a 2008-type Manny that put up a 4.19 FIP.
If there were 5 starters on the major league team right now that I could project to put up an ERA better than about 5 or 5.25, I'd be all for letting Parra try to figure it out and make a couple of good starts at AAA. That would maybe raise the likelihood of him getting his control back and reaching that upside. But it's just not practical for the Brewers at this point. Would you rather bank on Seth McClung, who has walked nearly as many (5 to 5.7 for Parra) and struck out fewer batters, and whose fielding-independent statistics suggest a mid-5 ERA? (Side note: in 2 starts, McClung's tRA is 9.8. Yikes.) I'm OK with giving Mike Burns a couple more starts, but I wouldn't project him to be better than Parra the rest of the way. And once we get into our stash of AAA starters with awful peripherals, I'd take Parra over Chase Wright or Tim Dillard every time.
The Brewers are in a pretty bad starting pitching situation right now. Despite working their way to a pretty good record so far, this is not a good rotation, in fact, there's only one pitcher in it that is even above average this year. The bullpen is good and the offense is good. But while Doug Melvin continues to lament the lack of available starting pitching, it would maybe be a good idea to stop punting games with replacement level or below starters when a alternative with a track record of success and an upside of a #2 pitcher is available. I don't have access to the information the Brewers do, obviously-- maybe there's a behind the scenes reason that it makes sense to leave Parra in AAA. Using the information I have access to, though, I would like to see the next start that Parra makes be in a Brewers uniform, not a Sounds one.