He hasn't got the speed of thought on a football pitch which is needed at the top level. His replacement last night had the presence of mind to try a 50 yard effort as he had a split second mental picture of what might be possible, which Barkley doesn't have sadly. I agree with you that calling him 'thick' is a bit below the belt but from a footballing perspective he's a second behind his peers.
What about the goal he scored again City couple years back? Pretty instinctive and opportunistic. Not far off the same level of quality of goal either.
Not that I really disagree with you though. In general he does need to think and act quicker (if that's possible for him) on the pitch. Though I do wonder if, with a bit more self-belief, that side of his game might improve. He always seems so nervous and that always inhibits instinctive play.