There's no question in my mind that Flutter is the best technologically speaking in the cross platform mobile space. The fundamental choices (namely low level drawing), as well as the teams incredible productivity, and superior developer experience put it well ahead of React Native. Its biggest failing and reason for 1000% less adoption than its had though, is that it's based around MaterialApp, they should have provided that as an optional layer on top of a bunch of un-opinionated base components. That has massively decreased adoption rate, users are straight away thrown into wondering how to create something with their own look and theme (try even extending Material theming) and so many just avoid it and go with something like RN which is has unstyled View, List and Pressable components out the box, to get going with something custom.