Earlier quoted context omitted.
Agree on most if not all points but the article didn't argue against any of that. It did point out two things. Companies don't have to literally be the only buyer in a marketplace to wield "monopsony power." If competition isn't perfect — like when there are only a few companies in a market and they aren't undercutting each other's prices — companies gain some ability to lower the price on the stuff they buy. Sellers…
Monopsony is a slippery concept. If I tilt my head just right, we could be discussing the way WalMart purchases products. They sell a product in their store, they decide they want a certain margin, and then they tell suppliers to meet a certain price target if they want their products in WalMart.
Imagine buying a nice desk to work on, and being told you could only buy paper and pens from the manufacturer of the desk. Maybe other vendors could be considered if 30% of their revenue went to the desk manufacturer. Preposterous, right? That's the world be live in and accepted as the norm for smartphones. Not a monopoly on a market scale, but the notion of selling someone a "platform" couldn't have really been foreseen a century ago. It's a similar idea, but it's more monopolism targeted at the market that surrounds the platform.
One particularly egregious example: Apple should reasonably be allowed to determine which products they sell on the App Store, but by preventing the installation of arbitrary apps from outside of the store, they've created a monopoly that they use for moral policing and anticompetitive practices. Apple not only disallows nudity-centric apps or apps that control nicotine vaporizers on their store, but effectively has banished them from their phones entirely. Which seems very suspect, and arguably they should not have the right to stop people from using what may be their primary computing platform as they see fit.
Then there's the issue of ebooks and music: Apple takes 30% of every in-app purchase, and developers are forbidden from using alternate payment processors to get around that. As such, Amazon can't reasonably sell ebooks in their app (you have to use a web browser and figure out the weird absence of buying capabilities yourself, as a user) since it would soak up the entire margin. Apple, however, competes with Amazon and sells ebooks themselves...which is questionable. Spotify cannot sign people up for their service without giving Apple an ongoing 30% cut of the subscription...meanwhile, Apple competes with them.