Hey when I wrote this article almost 2 years back I was heavily using flutter and now also continuing using flutter for apps I develop and push to my clients.
Still I would like to vote with flutter
from setup to publishing flutter is very easy developer friendly. and as you know from the latest flutter update 2.0 its no more just IOS and Android, Mac Apps, Windows Apps and Linux Apps are supported. and incoming years there is no doubt flutter gonna rock and make sound more than just cross-platform it will be portable-platform.
And while using Flutter web the major drawback i saw was it is not SEO friendly and Flutter web is not fit for content rich web apps I had migrate existing web app to react framework and honestly it was bit hard to adjust at first but it does the job perfect for web.
Also I learnt one thing "Its not about fitting all requirements in same Tech, When you see there is need of introducing different Tech welcoming it would be lot flexible and saves more developer effort"!
Both React and Flutter are good and doing their job just right!
Thank you for taking out time and reading this article :)