Yes, it is a major concern for all developers with apps in either app store. Whilst Android OS theoretically allows you to install apps from outside the Google Play store, Apple iOS most certainly does not, the ONLY way to get an app onto an Apple device is via the App Store, and if you sell anything via the app, they will no longer publish your app unless you accept Apple Pay and their 30 % cut of all revenue.
It should be noted that the 30% is not based on 'profit' but on 'gross revenue' - considering the processing fees for most credit card processors such as Stripe or Paypal run at 3-5% - paying 30% is gobsmaking.
We have a number of apps that we publish wrangling with this atm, our main challenge has been with Apple - they are insisting that we include Apple Pay capabilities or else they will not publish many apps.
This feels like extortion of the highest level, and it is the currently being contested in a major anti-trust case between Epic (the developers of Fortnite) and Apple, amongst others, the outcome of these cases will no doubt affect us all.