Iggy was never regarded as highly as Espinoza is now, and how has Iggy performed the last couple years? We also had Drew who was good in 2013 and Xander Bogaerts MLB ready and an All star now. We traded the best pitching prospect we had since Clemens for a guy on a career high, who has never pitched more than 150 innings in a season. We have 2.5 seasons of a guy who has never pitched more than 150 innings for a guy who has a better chance than anyone in the minors to be a true ace.
I get it, this is the price to pay if you're "going for it" but it's a steep price and I would have rather not paid it.