Except that you have artificially defined the market to be "applications on an iOS device" instead of "mobile applications".
By that definition Microsoft has a monopoly over XBox games, Tesla has a monopoly over their car apps, Sony has a monopoly over their DSLR apps etc, Salesforce has a monopoly over their marketplace apps etc.
Any antitrust action based on your definition would actually set a precedent that would unravel every single marketplace product. Hence pretty unrealistic.
Yes, and between Android and iOS, Apple and Google have captured ~98% of global the smartphone market in 2018.
Apple accounts for roughly 47% US market share to Google's 52%. Apple's app store generated 33 billion of the total 57.4 billion in revenue in 2018, with Google taking the rest.
They both operate app stores in very similar models, and both of them clearly need attention.
Just because two competitors happen to be splitting the profits from abuse doesn't make it any less of an issue.
I wish them the best while operating a distribution and marketing channel. I think it should be entirely illegal for them to prevent other channels from being created and installed on their systems.
To be clear - this is the definition of cartel behavior. They both operate walled gardens precisely because they know it makes a 3rd party breaking into the market an astonishingly small possibility, and they have both carved out a marketing strategy in the US that mostly doesn't overlap.