I'd agree - Apple handling payments/fraud/refunds and all the rest has value.
Where they don't have a value proposition is with the larger providers of content. People turning up and wanting to buy your product (and not caring how it's provided to you)
Same issue has been seen within PC gaming for many years - most consumers would quite happily add games to their Steam library - but Ubi, EA, Blizzard, Bethesda, Rockstar blah blah blah all nudge/command you to buy from their own shonky store.
It adds payment/fraud/refund etc only because providing that is cheaper than making sure developers pay their share after the fact. Benefits of a monopoly! Just think for one brief second how better the eco system would be by now if apple wasn't killing it via a monopoly. You are pretty much praising the mob that sells you protection because they gave you a point of sale that already subtracts their share.
That monopoly is so profitable that even TV manufacturers, kids toy manufacturers, etc now have a lock-in app store! Did you ever saw the marketing material for smart TVs development? I recommend you look it up. Their only 'feature' is 'captive users'.
Also, on your other over-simplified example, online gaming stores didn't solve any problem for the old consumers. Most of them still buy games despite the online systems like steam, while crying about lack of physical copies. What it did was unlock a huge market of non-gamers that didn't bothered to buy before.
