I would suggest reading some history rather than economic fantasy.

It's not "a competitive environment" just because it's legal to found a company if anticompetitive tactics are allowed.

You can start a railroad, but if the big existing railroads that already have lines running to the cities and factories refuse to let you connect to their service, your company has no hope of surviving.

You can start a factory making paperclips, but if the incumbent has billions of dollars in reserves and can afford to sell at a loss or barely above cost you will never be able to grow and thrive.

You can make a lot more money talking to your competitors and agreeing to fix prices or to each operate in regions that happen to not overlap, eliminating competition.

You can tell customers that if they want to buy product X that they want, they have to buy a bundle that includes Y, meaning that any competitors to Y are bound to fail since customers are already buying that version anyway.

This is just the tip of the iceberg. "History of antitrust" will give you any number of real world examples.