Apple clearly has a monopoly on the sales and distribution of iPhone apps, and as evidenced by Spotify, they are wielding that monopoly anti-competitively.
"Just use a different smartphone" isn't a real defense in my opinion, any more than "just use a unix workstation" would be to Microsoft's desktop computer monopoly in the 1990s.
Comparing Apple to 90s Microsoft is a bad analogy. Apple has like sub-20% market share of smart phones. Google/Android is the 90s Microsoft in the smartphone market, not Apple.
Comparing Microsoft to Apple in the 2010's is a bad analogy. Microsoft tried to bundle a web browser by default. Apple outright bans competitor apps and takes a cut of almost every transaction that happens on the device.
Consumers have a viable and realistic alternative in Android and 80% of consumers choose to use that alternative. Consumers did not have a viable and realistic alternative to Windows in the 2000s.
My point is that Apple and Microsoft are different situations. You can't look at just the market share and ignore the other dimensions where they are arguable behaving worse than Microsoft ever did.
The illegality of what Microsoft did with Internet Explorer was contingent on them holding a monopoly on personal computing. They were using their monopoly as leverage to obtain other advantages. Apple does not have a monopoly on smartphones. Looking at marketshare is essential.
"Just use a different smartphone" isn't a real defense in my opinion, any more than "just use a unix workstation" would be to Microsoft's desktop computer monopoly in the 1990s.