Interestingly the top benefactor is Google, as YouTube is #1 for subscription revenue in 2019 according to TechCrunch.

Subscription revenue on Apple's store was $3.6B of ~$50B in 2019, so 7.2% of app store revenue overall.

It's absolutely true that Apple doesn't have a lot of pricing pressure on their 30% fee, since their platform is so compelling and especially since most competitor App Stores charge the same amount. But it's also absolutely false that they have never lowered their rate.