You are really using Duffy as the player who he stood in the way of? Because other than him, all other players were 1st choice above him, and Alcaraz was back up, nothing more. Had Duffy stayed, he would also have been back up, and as a younger player in the key period of his career, surely leaving to be 1st choice in another team is more beneficial?
Regardless, I maintain that Alcaraz, Kone, Joel and McCarthy were exactly what they were intended to be. Players Martinez knew to help the transition with the dressing room. Alcaraz was a free transfer, and was signed as back up to help fill the squad where money could be better used elsewhere.
I would argue that Alcaraz was a much better player than any of the following... Anthony Gardner, Phillipe Senderos, Eddy Bosnar, Ibrahim Said, Li Wei Feng... All of whom were signed under similar circumstances under Moyes. The joys of a tight budget.
Also, you claim that he only had 1 good game, and listed a different game to the clean sheet debut game, which he deputised with another young debutant, away a at a difficult Stoke.
Blame him all you want for Kiev, it won't change that he was nowhere near as bad a signing as you suggest, and was in no way more culpable than the rest of the team on the day.
Pity we didn't sign him from Scotland, you'd be chairman of his fanclub now.