There is also another factor that isn't discussed as much and that's when companies become spread too thin. When a large company attempts to compete in every market, it will be increasingly difficult to be competitive in any of them. Yahoo is a great example of this, they spread themselves too thin, they didn't do any one thing better than others, and over time they were overtaken by competitors.

There is literally not enough data to make the point you are trying to make. All evidence available, which isn't much, shows big companies are destined to fail if they keep expanding.