> Leveraging your monopoly to compete in another area is illegal. Leveraging a strong position isn’t and Amazon is a long ways from a monopoly.

That really depends on interpretation, which has shifted over time and continues to shift. IIRC, recent interpretations of some types of anti-competitive behavior have been rather literal and required something very close to a literal monopoly, which has had the effect of neutering antitrust law in all but the most blatant of cases.

My understanding is that it's arguable that it's anti-competitive to leverage market share advantages more broadly (e.g. antitrust law could be used to constrain/break-up a duopoly).