[unclebucknasty]

>does that create a negative outcome despite clearly delivering a better product for customers in the short run

Yes. Nearly by definition the consumer generally benefits in the short run, which frequently contributes to the establishment of the monopoly in the first place.

The crux of antitrust law is concerned with the negative long-term effects, which frequently do lead to customer harm: lack of choice, price gouging, stifled innovation, etc.