Politicians should not have power to rule. There are 1 million ways to benefit indirectly from favors to lobbies, do not be innocent. Sometimes demonstrating corruption is really difficult.
You are worried about business that give people improvements or products every day, but you are not worried about regulators that twist stuff to get benefits without producing anything for people and that tax the people that produce?
I always found this view strange: someone that has nothing to do with benefiting others telling that they are good because they f*ck up the people that benefit societies. Yes, they do. Yes, not because they are good, maybe because there is mutual interest. No problem.
Do not tell me about corporations that have monopolies or a lot of power. All those come from absurd regulations. In the absence of them, things would be better. And more fair.
Maybe it is you who wants politicians to regulate.
I want them disappeared as much as possible and that they work giving service to others, not f*cking the very pillars of the benefactors of our society, which are business that produce something useful, by taxing them and imposing obligation after obligation, and, when they are friends, giving them competitive advantage via regulations with excuses to protect this or that, absurd regulations that only have the incentive to exchange favors, making effectively non-viable ideas and business that could succeed and improve all people's lives and remove government handouts.
The people that should govern should be people specialized in the tasks they do, and those tasks vary, in my ideal world, from nothing to security + minimal laws (do not kill, do not harm).
All the rest is giving them reasons to accumulate power that only is misused to polarize people and to give advantages to friends.
So, the disproportionate power that corps. may have is an issue of equality, but that's not this kind of corruption, at least not directly.