Coming from React I never trusted React Native as a mobile development framework. To me, using JavaScript for mobile development is too hacky and there are always some performance issues or other issues with those frameworks. Flutter seemed a lot better, and learning Dart is easy for someone who's used C# at one point or another (or Java or any typed language). Flutter in itself is much like React. You just treat it like a front-end application and it's very easy. Flutter also compiles to native code, so it's always gonna be more performant. However, I would not touch Flutter as a web framework.