Firstly, I justify my claim that Clark is weak through watching him play. Through you stating that he wins 60% of aerial battles has emphasised my point! He is not commanding enough. I really do not get what you are trying to say about him being a 'play-making' centre half. I would much rather a defender who can defend first and foremost.
On the deck - I am not denying that he is capable, or at least more capable on the ball than other defenders, but you rarely see him make crunching tackles - such as Baker.
All defenders can be caught out of position, no player is infallible. However, Clark is caught out of position on a number of occasions. Play often bypasses him because of his poor aerial ability and because I do not think he is commanding enough to consistently go in and win the first ball.
Ultimately, I think Clark has failed to quite live up to the promise made about him. He is an average defender, who might be better than average alongside another more commanding centre half. But it cannot be denied that Clark, along with the rest of the defence, is strongly accountable for our recent form.