I agree 30% is steep. I would be more inclined to say 20%, but remember that is for the first year. Its 15% after that. Most products don't make the lion's share of their profit in the first year because it takes time for them to get well know. Only companies like Spotify or Epic who have hype over products before they launch will see it truly affect their bottom line the first year. and remember this isn't a purchase, its a service. It's like a masseuse going into a resort and saying "I'm going to do massages for your resort guests in your lobby that people will pay for, but you don't get anything for it."
If these companies were smart, they would just follow Apples rules, then do what every other company does; create a non-profit coop ad campaign that educates people on the need to "support developers" not "big business" by subscribing to services from their own sights. It worked for Johnson and Johnson, Coca-cola, Bacon, etc.