> Walmart + Amazon combined are only ~16% of the retail business.

of ALL RETAIL? That includes groceries! That's huge! Anyway, Amazon is >40% of e-commerce & Walmart is >10%. Together they control more than half of all online commerce. That's definitely monopolistic.

> It was not already a monopoly. […] shortly before your noted date of "regulation" those competitors held the majority market share

From Wikipedia: "AT&T controlled over 80% of the U.S. telephone system market by 1907 and Theodore Newton Vail rejoined the company as its President. Vail negotiated with competitors, charging them fees for connecting to AT&T's long-distance network. These practices led the Justice Department to attempt to breakup AT&T, but a settlement was reached through the Kingsbury Commitment on December 13, 1913. It brought federal oversight into AT&T and led its Bell System monopoly to become federally regulated."

They had an 80% market share pre-regulation. Yes, it was already a monopoly.