A large government has far more opportunities for graft and corruption than a small one.
That is a good point, but as I see it, having a smaller government would mean fewer congressmen to bribe to reach a majority vote, allowing the company to expand its influence for the same budget. If you meant "small government" figuratively, you are right; a large government tends to have far more public projects to try to push through congress. However, without these, they would then focus their attack on public policy, resulting in additional lobbying against regulation and anything else detrimental to business yet necessary to ensure the rights and safety of the people.
Regardless of the literal and figurative size of the government, however, lobbyists had, have, and will continue to have more influence than entire political parties IMO.