Well frankly neither flutter nor react work well with complex UIs. They are great for simple things but they never worked for me for larger projects. And the idea of the same UI working in all OSs doesn't really work for me. Users of different OSs require different UI behaviors.
Or maybe it's just me. At this point, there's too much baggage in my past to give flutter another chance. :(
Yeah I actually don't see a lot of complex UIs written in flutter. The flutter gallery looks pretty complex and nice. https://gallery.flutter.dev/#/
But that's about it. Fluffy chat is a pretty good Foss app written in flutter but not as complex as Amethyst.
It always gets nuanced with "large projects" but Flutter (especially with the new rendering engine) easily handles a project the size of Amethyst. I worked on bigger projects. It definetely doesn't suck.
IME, differences between Android & iOS in terms of UI will be less than 5% of the codebase.
It's probably you, but that's okay! We all have our biases and preferences.
