I think this assumption that cross platform UI solutions can’t be extremely fast is a very strange one.
There have been some bad efforts at this in the past which is maybe how you arrived at the conclusion but the concept of Flutter is pretty straightforward and not dissimilar to games in some sense where you just need to push pixels to a screen.
They even have a some game engineers who used to work at EA on the team. One even wrote a popular book on it https://gameprogrammingpatterns.com/
Like in short, Flutter is going to be fine. It compiles to native code that just needs to push pixels to a screen, it has a bunch of smart people on it and some extremely heavy incentives to get this right.
There have been some bad efforts at this in the past which is maybe how you arrived at the conclusion but the concept of Flutter is pretty straightforward and not dissimilar to games in some sense where you just need to push pixels to a screen.
They even have a some game engineers who used to work at EA on the team. One even wrote a popular book on it https://gameprogrammingpatterns.com/
Like in short, Flutter is going to be fine. It compiles to native code that just needs to push pixels to a screen, it has a bunch of smart people on it and some extremely heavy incentives to get this right.