In my opinion, both lead to monopolies and oligopolies.

Ekianjo is right, in the sense that entities with lots of capital will become rent-seeking entities in over-regulated/mis-regulated markets because of very high barriers to entry. Examples include ISP's and insurance markets.

You are also right, in the sense that entities will rush to control a heavily de-regulated market. To that end, companies with lots of capital can afford to outspend or acquire their undersized competition. Examples include Air-transit post-1978 and the Internet 2.0.

There isn't one single legislation that led us here and there is no one-size-fits-all solution that can solve each monopoly. We have to evaluate each industry and each market on its own to determine how the state would break the oligopoly.