Tom has been really quick to say in past interviews/blog entries that past performance is never to play into a decision about who goes home. And while they'd love to keep someone because they've shown good skills in the past, if they messed up this challenge more than anyone else, they still go home. Tre comes to mind. Tre was an awesome chef, and went home for a challenge where he was the lead chef. someone else screwed up on his team, but he went home. He was measurably better than pretty much everyone but Hung (I think that's the right season-too lazy to look it up), but this particular challenge, this particular thing sent him home, even though he was really good.
Not trying to defend them, and I'm sad that Jamie went home because she was my favorite and I really wanted to see her kick Stefan's butt, sadly - not to be.