Except every platform ever built is there to get an unfair advantage. That’s the endgame for all the companies. Why would you build a platform otherwise? There’s a perpetual growth expectation after all.
Going so far as to clearly make an unfair advantage doesn't make sense if your platform is already printing more money than you could reasonably spend. As is the case with Apple, and with Valve. Music sales are probably a drop in the ocean compared to what they make on hardware and the appstore overall. They just got greedy and started acting like assholes when it came to their competition.
I think we can all find examples when platforms were not "greedy" and eventually got pushed out as irrelevant. That's why Apple and others will try to leverage their position to promote their new services.
Anyway, businesses might have that kind of aspirations but thats why we have governments. An important argument against influence of the businesses in the government and libertarianism.
That's not a problem, there's no inartistic correct amount to make for enabling or providing value. For 30 years now, software makes much more than that as numerous industries no longer employ people but software.
The problem is, when you own the platform and you start competing on that platform you have an advantage that can be misused. For Apple, the advantage that can be misused is to deny some API or the existence of competing businesses on their platforms. They can also do unfair pricing, for example it could be argued that %30 on Spotify is unfair when Apple has directly competing product.
For Amazon for example, they can have analytics on the businesses on their platforms and create competing products and promote them unfairly.
There are countless examples of Amazon doing this. Google was also fined many times for using their dominance in one area to force dominance in another.
Essentially, it's the good old platform owner getting greedy issue.
IMHO we need platform and product separation rules, similar to the Hollywood rules on separation of production and distribution.