At the time of the deal, it wasn't so obvious. Kelly had a 3.25 ERA with STL over 266 IP. Granted, it was just a 102 ERA+, and his 1.38 WHIP was not pretty, but he was pretty highly regarded. He was just 26 and could/should have been expected to get better.
Lackey's value to us was zero for the two months of the year we dealt him, but his next year with us might have had value and his 1.3 years of control to STL was very valuable.
Allen Craig had an .839 playoff OPS over 118 PAs. He was coming off a major injury from the 2013 WS vs the Sox and had a terrible half season with the Cards before the trade, but at age 29, I don't think anyone expected a cliff dive on his behalf. Only 22 MLB batters had more PAs AND a higher OPS (.863) from 2011 to 2013.
Look, I realize GMs are judged in hindsight. I get the reasoning for that, and I don't necessarily disagree with that realization, but at the time of the trade, it wasn't widely viewed as a gross overpay. 4 years of Kelly and 4 years of Craig at a $6.2M luxury tax cost for 1.3 years of Lackey, of which the 0.3 was useless to us was somewhat reasonable.
At the time of the great purge, I argued that we should have gone for more prospect types and not ML ready players/prospects, but the Sox brass was not about to look like they were packing it in for the next year. They wanted to go young but not too young.
I thought we could have done better on all three of our SP'er trades at the time, but to me, the Lackey trade looked better than the Lester and Peavy deals. I had high hopes for Kelly and thought Craig would at least be a good platoon player at 1B, LF or DH.