Google GWT and ecosystem is dead even though it was greatly popular - today nobody consider it to make a new app with that. Same with Facebook Parse - once Meta stopped supporting it most people don't use it even though it was open sourced and seems community still work on it - instead people use Firebase or Supabase.
Flutter is more complex and more ambitious than GWT or Parse - it has currently 12k+ open issues, imagine how many developers you need to resolve all of those. Without Google support Flutter would be practically dead - no company would consider it for any serious new project and instead would go with React Native, PWA, unity, jetbrain compose multiplatform
I tried GWT years ago and it seemed clunky. It reminded me of Swing and SavaJe. Learning Flutter now, which seems vastly better. as you point out "more complex and more ambitious" but also seems much more ready for creating end-user-facing software.
Flutter is more complex and more ambitious than GWT or Parse - it has currently 12k+ open issues, imagine how many developers you need to resolve all of those. Without Google support Flutter would be practically dead - no company would consider it for any serious new project and instead would go with React Native, PWA, unity, jetbrain compose multiplatform