There are definitely a few with UX problems, and there are a few apps completely missing - like ProtonMail - but overall bringing iOS and iPadOS apps into visionOS feels pretty natural.
If visionOS is to succeed, that's how it will do it. visionOS and iOS/iPadOS will continue to be developed in parallel, with new UX conventions slowly making their way to the traditional devices. Over time, apps built using Apple's platform will "just work" in visionOS as well.
In fact, while I hadn't thought about it until now, that's probably exactly why they're doing a visual refresh of iOS 19. Reporting seems to emphasize the "visionOS style" widgets, and it's apparent to me at least that that's going to lead to deeper and more complete integration between the platforms.
I don't think Apple is done with Spatial Computing. I wish the Vision Pro had done a bit better, especially its native software ecosystem, but I don't think it has been a failure at all. There were likely lots of reasons they launched it: to test the market's readiness for the product, to introduce new UX conventions, to get direct user feedback, to allow developers onto the platform, etc. They didn't have to make money on the Vision Pro (though, I think they did).
People here are always saying how hard it is to build a hardware startup; how just _shipping the product_ is a milestone that most of them never reach. Hardware is hard. I see the Vision Pro as Apple applying Agile to hardware. They shipped an MVP. It's not a "VR headset", it's a "Spatial Computing device". That lets them see how people actually use it, refine, and iterate.
The only reason you don't see this approach more often is that most companies have neither the capital nor the risk tolerance to do it. Apple spent $30B on R&D in FY2023.