It is still outrageous because those two big ones make a huge economy of scale. They did not develop a payment method for a single app but for millions.
Services are frequently priced by value to the buyer more than by cost to provide the service; I don't see a problem with that.
I think what's more outrageous is that more devs don't find it worth to do a website yourself and get a 10x cost reduction on transaction fees
Which is even better now that it’s 15% for small business