You seem to assume that mergers and acquisitions are not an essential part of a market economy. Left to their own devices, capitalists will always end up trying to form monopolies. You need a strong regulatory state to keep them in check. But then because they are inexorably pulled towards maximizing profitability, they will try to capture the state and deregulate. So, unless you go to a very aggressively anticapitalist set of policies a market economy will never be “functioning” for long.