The free market cannot prevent or control "over-sized Companies". "Over-sized Companies", or as I like to call em, monopolies, form when there are high barriers to a new firm entering the market. If a company does things to prevent other firms from opening, it would be harming the free market and is bad for both consumers and GDP. If someone were to invent a miraculous device that could cure cancer, and patents it, that person would have complete control over the market for the cancer cure. This means that that person could charge a much higher price than many could afford and would inevitably end up supplying less than society needs. A free market could not prevent this as there would be no oversight (price ceilings or quotas imposed by the government) in a completely free market.
However, monopolies created by a free market aren't always all bad. For example, it is difficult to start a power company because before you could provide power to peoples' homes you would first have to build a complex and expensive network of power lines. It's not exactly a built-out-of-the-garage type of business. In this case, a monopoly can be a good thing because it would simply be inefficient for more than one company to build power lines. And if two companies had their own power lines they would both have that "fixed cost" of building the power lines but have only half the customers each. This means that the prices would be higher in a competitive power market than a monopolist market.
In conclusion, to say that the free market is inherently bad because of its inability to control monopolies would be to ignore all of the benefits of a free market. In that vein, to say that monopolies inherently good or bad would be a misleading generalization. This is why every country has aspects of free markets and aspects of command economies. Do not let the polarized political climate of today trick you into thinking everything is so black and white!