React Native did a lot of work with the performance issues. They have now their own JS interpreter called Hermes. It also allows your javascript code to be compiled to byte code for better performance. Furthermore their new architecture allows for better integration with native and faster performance. https://reactnative.dev/docs/new-architecture-intro

I think a lot of people have their opinions based on an image of React Native in the past. It evolved a lot to be better performant and easier to work with. And for many people the React ecosystem is way more familiar than Dart.