No, imagine you have a electric toothbrush, and the brush head is proprietary, you have to spend $50+ for a new brush made by anyone, and Apple is the only place to get it. Apple takes $30 off a brush purchase regardless of who made the brush.
You can get a different electric toothbrush, but you can’t find one that you like more than this one.
This is called vertical integration, and this is where the regulators step in to mitigate market power imbalances.
The point is, with iOS apps on iOS devices, there are no alternative distribution channels, thus Apple can charge whatever they want because there is no competition in that specific market segment.