While in this case, Google is very likely abusing its dominance to coerce the whole ecosystem beyond their own platform in their favor: if the web becomes “works with Chrome” everyone is (probably negatively) affected.
1 : ten thousand
2 : a great number
The Apple/Google duopoly does not constitute a "myriad of competitors".
Epic says this is not a real factor for consumers, despite it still harming them.
Not only did Apple invent the modern smartphone, they created the first modern App Store. This, combined with their high cultural cachet, allows them to define by their actions what an App Store "should be" in many people's minds.
Personally, as a lifelong Apple user, I'm both concerned about Apple's singular control over the iPhone app market, and concerned what would happen if that singular control were broken.