It's an interesting perspective, but as I understand this case, the case is not interested in a developer's bargaining power against their distributor. The case is interested in the impact on consumers (fewer choices, higher prices). There's certainly no argument to make that consumers lack a variety of apps and app features.
I care about you as a developer, but I'm not sure this case does. Maybe I'm thinking about it wrong.
I think these are two sides of the same coin, because ultimately developers must pass the extra costs to users. The devs aren't subsidizing the 30%/15% cut, it's a tax that users pay.
App Store rules and the greedy cut also make certain kinds of apps and lower-margin businesses impossible to create in such environment, so this blocks innovations that could have benefited users.
When Apple bans competitors, blocks interoperability, drags their feet on open standards, and gives their own apps special treatment nobody else can have, then users miss out on potentially better or cheaper alternatives. This helps Apple keep users locked in, not innovate when they don't want to, and overcharge for services users can't replace.
All of that was more forgivable when smartphones were just a novelty, and digital goods were just iTunes songs. But now a lot of services have moved online. Mobile phones have become a bigger platform than desktop computers, and for billions of people they are their primary or the only computing device.
I care about you as a developer, but I'm not sure this case does. Maybe I'm thinking about it wrong.