You've confused some things. "Economic efficiency", as espoused by Bork and the rest of his Chicago School crew, came as a result of consolidation. His argument

You've confused some things. "Economic efficiency", as espoused by Bork and the rest of his Chicago School crew, came as a result of consolidation. His argument against strong antitrust enforcement was that it lowered economic efficiency to benefit smaller non-monopoly companies. This of course was a disaster for the American economy and it's taken 30 years of increasing corporate concentration for the politics to finally swing back against monopoly.