Of course many prosecutorial decisions are political. How could it be otherwise?
Even if political factors are not directly involved, one of the best stepping stones to higher political office is to make a name for yourself as a successful prosecutor. Thus every prosecutor has an incentive to care about his success in the public eye more than justice. Which is not to say they all follow thru on that incentive.
I would suggest that the pretense that prosecutors are not political, like the similar pretense about the media, has done more harm than good.
Interesting take.