I think it is over simplified and unfair. KPK is limited both on the number of case it can handle per year and to cases were the suspected State Loss is superior to Rp 1 billion.
A case which would involve less of a billion of State Loss can NOT be handled by KPK. Such cases are far from being rare all over the archipelago and are in fact a large proportion of the number of cases investigated. Yet, I doubt that a majority of them hide a political motivation to explain their investigation. It doesn't mean that none of them are, but the assumption that they are almost always politically motivated seems unfair considering that POLRI and AGO will instruct the majority of corruption cases.
For you to have a better perspective, here are some 2015 figures (Sumber: ICW):
Total number of Corruption cases for the year and for the whole archipelago: 550 cases
Number of cases handled by AGO: 369 cases
Number of cases handled by POLRI: 151 cases
Number of cases handled by KPK: only 30 cases
I think that you would agree that it would seem odd to say that out of the 550 cases 520 were certainly politically motivated because they were not handled by KPK. Many were genuine corruption case with a substantial loss fot the State and no obvious political motivation.