But that is a frightening conclusion for the science of economics. If the outcomes of a national economy depends on so many factors, then in the words of John von Neumann, "With four parameters I can fit an elephant, and with five I can make him wiggle his trunk." Of course, engineers are used to working with way more than 4 or 5 degrees of freedom but I get the heeby geebies at about 2.
I of course come from the school of thought that sees nothing wrong per se with a company with a huge market share but I believe that they have the power to use that market share to allow it to compete in ways that have nothing to do with efficiency. Also, an inefficiently made safe product is better in some case than an efficiently made unsafe product. In any case I think any broad single sentence social reform is doomed to failure.
The problem with economics as a "science" is that there is no control group. You can't, after all, create the conditions to collapse one economy while holding another economy constant to see what happens.
Plus, the models that usually - but not always - work are based on observations that usually - but not always - hold with assumptions that are usually - but not always - relevant. The problems with the models are that at times of stress, they often do not apply as the tails of the distribution become "fat."