Dart/React for a full fledged social media app in the short term and long term?

Hi folks, I'm building a social media app on Dart. I've been working on it for some time but it always bugs me whether I'm making a right choice by picking it over React.

Right now my plan is to build an MVP, apply to YC and then maybe keep Dart long term. Also, Our team is more familiar with Dart than React. We need a language which can work cross platform and is simpler to implement features.

Thoughts.