Barton and Fleck are too similar in style. Both like to play deep, taking the ball off the back 4 and starting attacks that way. Playing both of them means the midfield sits too deep, especially playing a 4-4-2.
Thats no different to playing Thomas and Fleck in the centre together and bar bringing Jennigns back, the only option is to replace Thomas with Barton. I like Barton, just needs a logner run of games and a bit of faith shown in him.
I don't mean to knock Thomas and I really hope he improves as a player but I am yet to see anything so far in his career for us to suggest the hype and "Liverpool thing" was justified. He gives the ball away far too often for a CM.