Its just crazy to think that you need to build an app three times, with different technology stack (react, swift, flutter) different UI frameworks, differen people.. While in the end it renders to the same pixels on the screen.
I do see a bright future for flutter. And its already used in some very big apps.
On the other hand: If you dont want to risk it, yeah then be prepared to pay 2x to 3x more on mobile development. And slow your development speed.
Too bad that flutter for web is just to slow and has no SEO support.