I agree that creating custom and complex cross-platform UI is the area where Flutter is really shining.

And the real pain point is business logic layer. For it Dart is not strong or safe enough. I would like to have some possibility to have, let's say, BL layer written in Kotlin for both iOS and Android, and UI layer written in Dart with Flutter, but for now this interoperability is not good enough, so the overhead will be too big.