Kudos to Google
In the early days of Play Store, app developers would tell us, "We're on Play Store, Google is doing our marketing, why do we need you?" Now they have conveniently forgotten about that and are trying to pretend that the only value provided by Play Store is payments, which others provide for 3-4%. By giving a takeoff of 3-4 percentage points for alternative billing, Google is making it clear that it also charges only 3-4% for payments and reminding them that, while they're free to take their payments elsewhere, they still need to pay for marketing and other value provided by Play Store. Fair is fair.