Does the consumer even really win? Once Amazon/whoever has a monopoly, they get to decide when and how to innovate, and the prices. Is the product now as good

Does the consumer even really win? Once Amazon/whoever has a monopoly, they get to decide when and how to innovate, and the prices. Is the product now as good and as cheap as it could have been with more competition? Their PR and lawyers will say “yes” and who can prove otherwise?