The only two words needed to understand this trade are as follows.
"Sellers. Market."
We needed starting pitching and everyone knew it. And starting pitching is the one thing that is never out of demand. No team is going to cut us a break in that circumstance so anyone we got would cost us something we don't want to lose. Of the available guys to lose, a very high potential A baller is one of the better choices. Of the available options of who to get bent over for, Pomeranz is a surprisingly good choice, I like the way DD is thinking here, he's got the demonstrated skillset to be durable and reasonably effective, and anyone better established than Pomeranz would be even more expensive.
I'm also glad that we picked up someone reasonably young when we're trading top prospects away. We won't have much direct control over Pomeranz, but if it works out, he's young enough to re-sign and that's a good thing.
I get that Espinosa is a potential stud, but we don't need potential right now. We are in range of a playoff berth for the first time in 3 years, this is absolutely not the time to be penny wise and pound foolish with our prospect pool. We absolutely could not fail to trade for a starter, doing so would be tantamount to throwing the season away. Since we were officially desperate other teams were going to ask for the moon and stars for anyone we picked up. This is the best deal DD could make and a better one than I could have thought of if I'm being honest.