You've answered your own question with what's bolded. If his ball winning makes no difference, than of what value to Carlton is that ball winning? Why isn't he playing in such a way that makes his poor forwards better? There's way to do this. He himself could be a better ball user and not commit 4 clangers a game despite hardly kicking it, he himself could be better at thrusting the ball with his low metres gained stats. He himself could make the forward line better, by having the ability to be a better resting forward, mixing it up to give the opposition defence something to think about and attract attention as a forward making it easier for his teammates.
Think of it this way - if you put Bontempelli instead of Cripps in Carlton's team. Yes, he would win less clearances and probably an even higher percentage of those clearances would go to waste. But Bontempelli is a much better kick, has much more attacking instincts to get the ball moving forward, will attract attention as a ball mover because he's a better ball mover (ie teams zone off Cripps' kick and zone onto the players he tries to handball to, therefore putting pressure on teammates), and has the ability to be a psuedo-key-forward whilst resting up there, which Cripps cannot do (majority of Bontempelli's 20+ goals last year were as a genuine resting forward, not from midfield, both goals he kicked against Collingwood Friday were when he was resting forward). Bontempelli averaged 4 and a half less clearances per game than Cripps, but spent about 1/3 less time in midfield - adjust for that and Cripps only averages 2.5 more clearances than Bontempelli. Is 2.5 clearances worth more than everything else that Bont offers that Cripps doesn't?