But from a pure business perspective, if they're charging on an annual basis, if the average subscription length is say, 4 years, after the first year the rate is 15% not 30%. Additionally, Apple pays all the transaction costs, which on a $99 charge would be ~3.3%. That means if they go with Apple's system they'll effectively pay 18.75% versus 3.3%. Do they really think they won't achieve 19% [1] more subscriptions with a native signup flow and payment option compared to only recruiting customers outside Apple's ecosystem? That's what they need to break even on Apple's cut here. If they do think that, I'd be tempted to claim they don't really understand the power of App Store distribution.
[1] 96.7% revenue cut / 81.25% revenue cut