You could have a theory of antitrust that allows for both rules - if a company is across multiple fields of business or if a company is too much of a single field, it gets split up. So Standard Oil and Ma Bell get split up for controlling too much of their industries and using it in anti-consumer practices, and Amazon gets split up (AWS vs everything else) because it’s inherently too large and it’s better for the economy for them to be split up.
of course, but i'd argue that too much of a single field is usually a case of a company that's actually in multiple businesses (see the mcdonald's example in a sibling thread).
my simplified perspective is a melding of the brandeisian (big is bad) and the chicago schools (economic efficiency for the win!), touched on in the article, so i certainly have no problems with synthesis in matters of antitrust. =)
