Keep in mind that even if Standard Oil in no way benefited from specific government privileges, all large companies benefit in various indirect ways from regulations, especially corporate personhood.
A case could probably be made that without a state no company would have gotten so large at that time in history. The state’s hand was in it in some way, hence it would be counterproductive to hold Standard Oil or any very large company up as a spotless example of the free market in action.
Unfortunately, these kinds of evidence-based arguments can never be fully slam-dunk, because the state - like a cancer - infects everything with its distorting effects. There is no fully clean, fully free market example to point to. We should expect any company to be a little “evil” once it gets large enough, its bloat being fueled in some way or other by the tumor of the state.