Iced is a lower level GUI library, similar to what GDK is to GTK. We built our own COSMIC-themed GUI toolkit around iced, which is called libcosmic. As we’ve gotten more and more widgets and application logic developed, actual application development with libcosmic is a breeze. Even if you do have to create a custom widget, it’s much easier to creating custom widgets in GTK. We’re able to develop much faster than we ever could with GTK now.
Yew and Leptos aren’t comparable since they’re not native GUI toolkits. These are for web developers rather than application development. It wouldn’t be possible to use this for developing layer shell applets for COSMIC, either.