Even in free markets, Oligarchies and Monopolies are a thing. No system is perfect - potential lack of competition in niche areas is one of the weaknesses of a free market system.
But we choose a free market or whatever because we believe it will produce the best outcome. If it doesn't work as envisioned then we can either tweak it until it does work, or throw it out and start again, the worst option is to leave it alone, especially as we know it works elsewhere.
There seems to be a view that free market v socialism is a binary choice. Its a continuum, and both pure socialism and pure free market are equally bad. No country follows either path 100%.
