The jank issue has been fairly minimized with Impeller, so performance-wide, it's fairly on par with RN. The only 2 issues I seem to find are the core Flutter team leaving Google, and Flutter web being unstable (and honestly I just wish they stopped developing for web and focusing on mobile). Another issue is learning a new language, but Dart being strongly typed makes it much easier to work with than Javascript.
In either case, RN and Flutter should be used only for the MVP stage, and once you can, you have to immediately switch to building on native at the right time.