I don't... look Marco has some talent (he wasn't #1 on the STL prospect rankings two and a half seasons ago for no reason) but he's been a walking injury factory for 2 years. He's now back to being somewhat similar to Andrew Moore with a lot less durability. I know the Cards had some discussions about bullpenning him to try to keep him healthy, but he's a buy-low candidate that we just cashed in our biggest available chip for. O'Neill has been destroying pitches for a month, slugging .700+, and we traded him for a lefty who will probably be a pen arm in 24 months?
He only throws about 90 MPH and relies on location and changing speeds to be effective with his 5 pitches (like I said, think Andrew Moore except Moore has a hotter FB). With no endurance (he's thrown more than 80 innings in a season just once, and is at 74 this year) I don't know what Seattle is expecting. They're apparently sending him to AAA to hang out with our other not-good-enough-for-the-bigs pitchers and await his callup as a #6 starter.
Gonzales is local (Gonzaga grad, lives in Seattle). Maybe the Ms know something that can help him resume MOR form. But look: we traded Zack Littell for Pazos, and Littell is better than Gonzales IMO. We tradedd Gohara+stuff for a busted Smyly, and Gohara is way better than Gonzales. So in order to patch that hole we tossed one of maybe two power bats in the system (depending on Kyle Lewis's healing) for a busted starter with very little assumed value and possible position change on the horizon.
Again I'm going to call, "bad return on trade value." Dipoto might not care right now, but the Mariners will soon. Here's hoping the Ms know something about Marco (or O'Neill) that makes this make a lot more sense soon, because right now I just see it destroying Seattle's ability to make a serious addition either now or in the offseason. Losing O'Neill negates most of your trade packages for top-flight talent.
I don't think Gonzales is that talent, and he would rank below O'Neill in both upside and expected contribution for me. Still trying to wrap my head around it.