Seems to me
Apple's defence is we are $h1t at security, so we have to be careful who we let in.
Which provides no defence to the claim they are a monopoly and no defence to the fact they are exploiting this position to gouge their users/developers.
At the moment they charge exactly the same as google do, but the choc factory only has an effective monopoly, not a literal one.
the pair of them need to look hard at the service they are providing and the cost of providing it.
App purchase fees are listing and distro fees, so should not be more than about 12-15% (like Amazon Marketplace or e-bay selling fees) and as the volume goes up this comes down.
In-game items are payment processing fees, so any reasonable processor will be working on about 5% (see PayPal, SumUp, WorldPay, Stripe, ....) or less, at the volume they are processing.