Giolito is incredibly valuable. When was the last time a #1 prospect got traded other than Will Meyers? I can't think of any #1 prospect pitchers being traded recently. I think you undervalue Fedde, Lopez, and Robles. Robles has an elite package and is ahead of the curve that similar aged, just out of high school guys are on. He'll be a #40 something prospect this offseason. Lopez value has gone down since it peaked late in the 2014 season, but the stuff is still there, he's not old, and will not be too far away (AA to start the year). Jonathon Sickels actually still had him ranked #47 on hiss midseason prospect update, moving him up from #150 prior to the season. He could be a lockdown late inning reliever later this season with closer upside, and still has an outside shot at being a mid rotation guy. If he developed better control, he could be an ace, but that's a bit optimistic. Fedde will be a fast riser. He'll probably spend this upcoming season split between A+ and AA. It's al about getting innings under his belt at this point. So basically Lopez is not far away. Neither is Fedde really. Robles is, but his upside is significant enough to warrant the risk. I also think Wilmer Difo is not worthless.
I agree that Giolito's very valuable, but "very valuable" is still a long way from being the main attraction for getting Mike Trout, which was the original supposition. I suppose if there was more to go with him in that package, maybe, but the Angels specifically are looking to compete now, and trading their best player wouldn't do it. In the hypothetical world of trading this entire package for a single player, you'd need to be looking for a very valuable player on a non-contending team, preferably on a team-friendly long term contract (otherwise, why would you give up all the team control?). That doesn't exist too many places, although perhaps Rizzo's old employer would be one - although that would turn Zimmerman into one hell of an overpaid pinch hitter. As for the rest of the players, I don't disagree with your assertions about the players. The problem is that most GMs place a high premium on major league readiness.
Robles is a hell of a prospect. He's also only going to turn 19 next season. But he's also never been above short-season and low A. There are a lot of players who hit well low in the minors and can't replicate that higher up. And in some ways, his age is a disdvantage: with guys that young, teams sometimes worry about them filling out (which in this case they mean as a euphemism for "getting fat") too much. Robles is rather far from being fat by any stretch of imagination, but Miguel Cabrera was also skinny at 19. With Robles, you're basically asking how much a team would trade for a very high draft pick - the answer again is quite a bit, but not if they need help soon. Lopez's value is pretty uncertain: he's one thing if you see him as a starter and another if you see him as a reliever. Hard-throwing relievers with spotty control aren't that valuable; if the control is tolerable for a starter, you're talking Yordano Ventura, who may be a chameleon from one year to the next but is clearly a very valuable guy. If he had more than one incredible season under his belt, that's one thing, but again there's uncertainty: possibility of a one-year wonder, possibility that he can't do what he did in the very low minors at a higher level (indeed, he was OK but not spectacular at high-A). Twenty-eight walks and 93 hits in 99 innings in high-A doesn't scream "major league ready" at any point this season to me. Fedde I'll have to punt on a bit. I don't have as great a sense of how other teams might see him. He needs a lot of innings, and they need to be at higher levels. If I'm a GM trading for prospects, I'm going to be hesitant to buy the upside on players who haven't at least shown it in high-A over a full season. The jump from the lower levels is just too much to take for granted. My view of Difo is based on seeing him as a utility guy. I don't see him ever being more than a barely-adequate hitter in the majors. He needs more at bats, which probably means high minors to start next year, as much as I wish he were ready.
