You're going off on a tangent here. ANY concentration of power that takes away freedom is a problem - not just excessive government power.
I will agree with you that it's a problem when it's the government doing it if you will agree with me that it's a problem when corporations, oligarchs, plutocrats, the military and/or theocrats do it.
Of those, I would argue that too much government power in a society like ours is less of a problem than too much power concentrated in the hands of the other loci mentioned. Why? Because none of those have a constitution with a Bill of Rights that the people can use to protect themselves. Those other groups don't even have to pretend to be answerable to the people or pretend that people have rights.
Plutocrats, by definition, only become so through using the government to further their interests. This is what there is too much of. And it is enabled by the continued fallacy being peddled that corporations are the ones running amok. Corporations and private interests, regardless of size, are at the mercy of the market, unless they are able to embed themselves with government interests, which then allows them to skirt laws or place themselves above it. John Rockefeller, with Standard Oil at it's zenith, attempted with some other businessmen to form a private cartel...it failed miserably. Even with all his wealth and market share, he could not separate price from value and force the market to do what he wanted it to. Today, he just would have had to fund a few strategic campaigns to get regulation, tax code, ordinances, etc passed to accomplish the same goal and more. Progressives fear the Koch brothers like conservatives go crazy about George Soros...but what are both afraid of? Of them making really savvy investments and business decisions? No, in both cases the fear is that they have unequal access to government and will use that access to the detriment of individuals and the country as a whole. But, the focus goes to their wealth, when it SHOULD be going to what it is that we are afraid of them buying, and why we continue to allow it to be for sale.
Bottom line, corporations and individuals are going to use their wealth and influence to the greatest extent possible to enhance their positions. If their only real outlet is to develop a better product or service, then even if they continue to enrich themselves immensely, we all win. When they can buy politicians, bureaucrats, and regulators and throw up roadblocks to innovation, barriers to entry to the market, and create huge economic windfalls for themselves by rigging the system...they will do that too. The solution remains: Reduce the power that the government has to sell, and the resources that they have to mismanage and abuse. The notion that we just need to get the "right people" in there to manage the whole thing has been around forever, and is as misguided today as it has always been.
So, while concentrations of power can be bad in both the private and public arenas, concentrated government power is a thousand times more dangerous than that of private players, because it is a self perpetuating machine that is itself the most potent tool for private interests to hijack to their own purposes. And it happens every...single...time.