Most of the mistakes, IMHO, are cancelled out by his job of getting this team up for every game and having them play a lot better than last year.
But I agree with you in principle - Jackson has been hit-or-miss this year, but after he gave up the homer in the 8th, he clearly didn't have it.
But like DBAHO said, if Politte keeps mixing it up with his slider/change/heater, he's going to be as solid as he was for us early on.