I guess it depends on the app. Google's own apps on iOS don't strike me as feeling very native. I would think they'll get closer to nailing the Android behaviour. In a way these toolkits fill a space like Electron on the desktop where the developer won't, or can't, for all in on a native experience.

As someone who built some mobile apps with web technology I can see how Flutter would have an appeal because going into the project you've already given up on the native experience. There are still (unfortunately?) a world of marketing-driven apps with the brand overriding design choices which would be suited to this. Tools like Xamarin probably have a lead for line-of-business apps inside companies due to the MS ecosystem integration, but I could see people choosing Flutter for these apps if it's easy to build and maintain apps.

None of this changes the fact that for best-of-breed apps in a public store you'll need to use the native toolkits.