That's a practical solution, but IMO React is playing a fundamentally different game here, they have Native for mobile apps, and third-party (!) support for Windows and Mac (what about Linux?). Native doesn't even support the web, like React and React Native are two different things, they just share a somewhat similar UI framework basically.

Flutter on the other hand is architected as a solve-it-all solution. They even went as far as designing Dart rather than hacking a decent solution on top of JS and the current mess of web standards. IMO that's a much more interesting and powerful approach, that isn't fully ready yet, but if it ever becomes actually good I'll personally probably jump ship and use it for everything.