Lol SwiftUI/Jetpack/WPF aren’t design tools, they’re for writing native UI code. They’re simply not the right tool for building mockups.

I don’t see how design workflows matter in the conversation about cross-platform vs native and RAM efficiency since designers can always write their mockups in HTML/CSS/JS in isolation whenever they like and with any tool of their choice. You could even use purely GUI-based approaches like Figma or Sketch or any photo/vector editor, just tapping buttons and not writing a single line of web frontend code.