The contradiction is in trying to support the rules with one hand while resorting to the same bypassing tactics they decry when they're in the position of a business on someone else's platform.
edit: typo.
To me, that sounds like a compelling argument in a hypothetical anti-trust suit against Apple where a plaintiff is claiming that Apple's requirement to use Apple's in-app payment system for all payments in iOS apps is anti-competitive behavior.
Apple explicitly allows apps like Spotify and Netflix to use external payment processors on iOS via their developer guidelines.
They just don't ban the alternative practice.
Apples’s defense of its in-app payments rule is that having a single payment system owned by the platform used by every app on that platform provides the best experience for users. According to them, Apple isn't being greedy but rather they are ensuring their users have the best experience on their platform.
But if a single payment system for a platform is such a great user experience, why does Apple not offer that superior experience to their Apple Music customers on Android?
Of course, one could argue that Google's refusal to require apps on their platform to use their in-app purchase system means that superior user experience of a uniform payment system is out of reach regardless of what Apple does with their own apps on Android, so maybe it's not a contradiction after all.
Let X be "That other marketplace banning me from offering discounts is a violation of antitrust law".
Let not X be "Me banning vendors in my marketplace from offering discounts is permitted by antitrust law".
You get to pick one and only one position of those - but in most cases there's no conflict; you can ban some practice in your marketplace (and assert that this ban is permitted by law) while at the time doing the same thing yourself in other marketplaces which haven't banned it - as long as you're not legally challenging their right to ban that practice as well, if they should choose so.
Let not X be "It is okay for me to use discounts at another restaurant that bans discounts."
Let X be "It is okay for me (Costco owner) to require customers use CostCo credit cards only"
Let not X be "It is okay for me to use my non-Safeway credit card at Safeway"
Let X be "It is okay for me to ban my customers from using discounts."
Let not X be "It is okay for me to use discounts offered by another restaurant."
This doesn't feel like a particularly contradictory situation.
Maybe the issue is that we skipped a few too many steps, because there isn't anything particularly illegal about Apple only letting apps doing certain things (like not bypassing their store) onto their store. The issue is that this is occurring in a larger situation where there are concerns about being a monopoly. I wonder if we build out exactly why what Apple is doing might be wrong (basically the argument they are having to defend against by claiming X is okay) we can see it isn't an issue. But at face value it feels to be taking a very broad view of what constitutes hypocritical behavior to the point it renders the notion useless.