Here is why I'm hopeful. SwiftUI is as you say wonderful, but is very much a closed ecosystem. You can't really implement your own custom views, rather you can assemble the premade ones in various (cool and interesting!) ways. If you wanted grid layout before iOS 14, you were on your own.
By contrast, in what I'm building, everything is open-ended, and you are invited to build fully custom versions of every piece of the system - change propagation, async resource loading, layout, drawing, animation, everything.
So yes, I am hopeful this approach will give good results for especially those highly intensive applications you mention. And if not, we'll learn something why not. I'm looking forward to trying!