I'd also say that the write once support on all devices is definitely not a 100% thing. There is definitely a lot of tweaking for adding support to specific platforms and devices (think iPad vs iPhone vs Android Phone vs Android Tablet). I've also found it that its a lot easier (when compared to native development) to create code that needs to be heavily refactored out when adding support for additional devices while also making sure to not braking things on other platforms. This last point complicates development because then you are forced to be familiar on how to test and debug on each platform, making sure that changes or issues fixed on a specific one don't break the other ones; this for sure adds a ton of development and testing time, specially when you go beyond just android phones and iPhones.
Where flutter has shined for us though has been for internal tools that we deploy and for which the UI is not designer-driven or that don't have stringent design and performance requirements.
Now don't get me wrong; I'm well invested in flutter but it does not come without its compromises, specially on iOS being second in line support after Android. It definitely gets you quicker to market with an MVP on more platforms compared to pure native development.
A few years back I built internal apps at work using React Native. Warts aside, it was a great dev experience and was able to re-use code 100%. However, having to ensure all was well with both iOS and Android (and indeed sometimes there were edge cases) slowed me down.
SwiftUI and the Combine framework provides a similar dev experience I felt using React Native. Moreover, app previews in XCode make it straightforward to paint different application states and iOS settings. Building for one platform also reduces the quality check surface, allowing you to spend more time focusing on product.
If cross platform is a necessity from the onset (e.g. internal app for work where all employees need access but may have different phones) then starting with non-native makes sense. However I personally recommend anyone looking to build a product as an app to focus on iOS first and use SwiftUI. I reckon you will move faster, have a smaller code base, and a better app. All of which are conducive to finding PMF if you intend to make a business out of your product
Nevertheless I think your position is naive; most interesting and engaging apps need more information than you can get from a generic tool alone.
I feel SwiftUI markedly lowers the 'barrier to entry'.
Crossplatform tools may serve your purpose better, but I think it's unfair to say that, at least for SwiftUI, native development may not be as 'joyful'. A list view in SwiftUi is List {}.
It's so domain specific that IMO it's not worth trying to do that kind of work unless it's your main career. I ended up taking the app I had built down because I kept getting support requests for bugs I didn't know how to fix and the idea of going into the code to add more features filled me with a sense of dread. The app was doing somewhat well too, it had about 1000 DAU.
I built another app for the CDC in React Native, which has its own foibles but is overall much easier. I'm not sure how successful Flutter will be overall because you can't leverage outside skills and you have to learn a different language.
Flutter on the other hand, is a pure joy. Almost anything you need UI-wise is prepared, and you can just customize it the way you want (try implementing a ListView in native vs Flutter). For the big majority of today's apps native is just not neccessary, most apps don't need bluetooth access or some other specific service.
Especially from the business side, Flutter is way better. You need to maintain only one codebase which results in less need for resources. And you are way faster, you can iterate like crazy and push out an MVP...
And when stable Flutter Web arrived, it is game over...