I mean everyone's assuming that non-IAP subscriptions are going to be 30% cheaper but I don't really buy it. If the market has proven that someone will pay $10 for a thing, suddenly offering it for $7 seems like a bad business move.
The mobile app payment market hasn't been competitive for a decade, so Apple has never had to compete with companies that are more efficient than they are, and can offer the same or better service for less than a 30% cut.
However Apple does vet apps and focus on security somewhat (altho Google's project 0 seems to do a better job at finding bugs for Apple), however 30% is far too much even for what Apple are offering their customers.
In an ideal world, Apple customers need to be told: "you will be charged extra buying through Apple to help pay for the protections/quality that our platform offers you".
However, Apple explicitly disallows both telling users that they're being charged more and why, and that they could get it cheaper elsewhere.
Regardless of whether Apple are still allowed to charge x%, the first step it to get Apple to allow developers to tell the customer about other payment options and for Apple to explain to their customers why it costs more, then customers can make the decision for themselves.