Shaw was my "sleeper prospect" many years ago, but I guess I never really saw him as an answer to 3B. I saw him as a plus fielding 1Bman who might never hit well enough to play 1B FT.
I liked the trade, more out of my perception that our pen was our weakest (no weak) link. We had lost Uehara, Ziegler and Taz, and there was no way to know that Kelly's one good month to end the 2016 season was going to continue. Also, I don't think anyone expected Kimbrel to pitch like he did with the Braves. Barnes and Hembree and others have all done better.
In hindsight, the trade looks "unbelievably horrible" right now, but let's wait and see how Shaw finishes out the season. The Thornburg injury was not really foreseeable, but when judging by hindsight, GMs often look bad.