What’s Revolutionary about Flutter
Wm Leler

Flutter looks promising but right now it doesn’t perform well against React Native on my 4 year old phone (Sony Xperia ZL: Android 5.1, 1080p, 2GB RAM, etc — http://www.gsmarena.com/sony_xperia_zl-5203.php). 
React Native’s UIExplorer is butter smooth whereas Flutter’s Gallery takes very long to start and animations skip a lot causing bad user experience.

> Widgets are typically accessed quite frequently (up to 60 times a second during animations, transitions, or when the user “swipes” something on the screen with their finger) so this can cause performance problems.

Perhaps this is the reason why Flutter animations are slow, specifically Flutter is processing animations at 60 fps while calling the reactive framework (build method). That’s an architectural recipe for slow animations. React Native doesn’t do that, animations run outside the reactive framework (render method) and are completely managed by native code outside of user code so there is no way the developer can make a mistake and slow running animations.