lol.. gross margin and commission per level item are totally different. The big company buying a bulk item which reduces cost price and increasing revenue. This is software development which totally different and the cost is totally super high. Most would sale as volume purchase so can bypass the 30% margin from google/apple for the digital items. For non-digital items, apple nor google have no legal right to enforce it. Normal software charge dungeon of $$$ but when market going to subscription base which is volume license instead of sales of box e.g Microsoft, Adobe.Well, if you look at Walmart their gross margin is around 24%. Bookstores get even more. The rule of thumb was a product sell for about 3x at retail vs the what the producer gets; so yes 15% is a low markup. If you look at what markups there are in boxed software at each step of the process you'd find that the developer gets way less than 70% of each sale.
The problem is not Big Microsoft, Adobe but the indie developer. The coupe the nill return on investment(ROI) they add advert annoying to coupe with investment.
The conclusion is simple to see, apple in-app subscription much higher than android to coupe the cost not because of 30% but the cost of development, the long testing, rejecting. Apple itself doesn't follow proper User Experience(UX) but always try to delay the publish such as "Hey"