That article has basically been validated over time. At the time it was written, the argument was that monopoly is bad for consumers even if it makes prices cheaper, and that consolidation of producer market power needs to be understood as consumer harm in itself, even if prices or services paradoxically become better for consumers.

It’s no longer a paradox today, though. Amazon has raised prices and reduced the quality of service by a considerable margin, and uses its market power to prevent the competition from undercutting them, rather than competing fairly on the merits.