But don't necessarily write off iOS and "big boy" Applications. Apple now sells (rents) full-blown Logic Pro for iPad. $5/mo or $50/yr. And Projects can Round-Trip to-from macOS Logic Pro.
The very fact that they're able to do that, rather than having to sell the app outright, is prima facie proof of an unhealthy ecosystem with inadequate competition.
I've used Logic on the Mac, but I prefer Digital Performer. Others prefer Cubase. Only one of these three exists in its full form on iOS. The same is true across a wide range of products.
The problem is that there's no advantage to using an iPad over a computer for any of this stuff and a giant pile of huge disadvantages (limited screen size, limited storage, limited connectivity, etc.), so most users don't really want to use these apps on an iPad, so the developers mostly don't bother to port their full apps to iPad. And realistically, I don't see that changing any time soon.
As for the whole "App Store Only" on Mac thing not happening, if Apple thought they could get away with it, I'm pretty sure they would, but they couldn't, so they won't. They would have to go back in time and build the platform that way back in 1984, so that people wouldn't have thousands of dollars in software that can't be readily shoehorned into that distribution model.
But the App-Store-only model definitely holds back the iOS platform. If you could run actual Mac apps on iOS, all of those limitations would go away, and the iPad would be a viable second computer for a lot of people while traveling, and could replace the computer for a much larger percentage of people than it currently can. And the fact that Apple still hasn't recognized this and opened up the iOS platform is what makes me so certain that if Apple could somehow make Mac users stomach the idea of not allowing direct distribution, they would. Fortunately for everyone, there's zero chance of their users accepting it.