Or are large institutions such as the government, the military, and corporations such as railroads or energy companies or Microsoft more influential in bringing about political, social and economic change?
One of my favorite quotes is:
Never doubt that a small group of thoughtful, committed people can change the world. Indeed, it is the only thing that ever has." - Margaret Mead.
Yes, those organizations you mention do institutionalize the changes. But institutions on their own will never think of the changes. It takes a person, and then people. It also takes a lot of commitment. Change is one of the hardest goals a person can have. Those few who are able to keep going despite the resistance are the ones strong enough to cause change.
This is one of the enduring debates in history, political science, and other social sciences -- are "great men" important or are they not? One could easily make an argument either way.
I would argue that institutions are more important than individuals in shaping the world that we live in today. I think you can see an example of this in the struggles that Pres. Obama has faced in his attempts to bring about change.
If individuals were really that important, you would think that Obama would have had more of an impact. He is an impressive and highly skilled individual who ought to be able to have a great deal of influence. However, because of the power of institutions, Obama has not had a truly significant (I think) impact on American life. He has not been able to remake the system because there are too many institutions that have a stake in keeping things the way they are.
Perhaps you might consider the idea that individuals are important for driving things forward, but that they are often thwarted because institutions are a strong force for the status quo and these institutions tend to inhibit change.