Philippon and Gutiérrez answer a clear no

Politicians and activists are warning that mega-companies like Facebook, Wal-mart, and Amazon are returning America to the Gilded Age. They point to record breaking profits and mergers the size of small countries.
On the other hand, many  economists and antitrust lawyers aren’t panicking. They say innovation and better management are driving these so-called superstar firms to unprecedented levels of efficiency. Their size and dominance is just a side effect.
However, both may be missing the bigger picture. 
Read this interesting analysis by Philippon and Gutiérrez