That's valid, all the work that goes into cosmic also goes into the Rust application stack as well, so people are passively benefiting from this as well.

Plus there are only 2 Wayland desktop environments, the big 2 have to be challenged sometime.

If you want to turn into a COSMIC fan. Their app store takes approximately a second to fully load everything. Searches take on the magnitude of milliseconds to complete.

It's literally faster than typing flatpak install <app-name> -> y. GNOME Software and KDE Discover don't come close to this level of blazingly fast rust speeds.

They didn't technically build their own GUI stack, iced already existed and this was during the time where native Rust applications were being theorized about but no one really put pen to paper yet. So COSMIC acts as an example of what iced is capable of doing and what it needs to implement to improve.

LXQT comes to mind when leveraging Qt for the desktop and it certainly works, but KDE is much more than just a Qt-based desktop since it has its own components on top of it (like Kio, etc.) System76 is a hardware company so their principal interest is to ship an operating system that works with their client's hardware without any hiccups (or at least hiccups that can be fixed immediately by them instead of waiting for upstream). They can't afford to wait for GNOME or KDE to implement certain wayland protocols or desktop features that they know their clients already expect with their GNOME 42 spin. Wayland is reaching critical mass and they can't afford bargaining with GNOME nor switching to a C++ based KDE when most of their engineers use Rust.

It's a technical exercise as well as a pragmatic one. If you have the resources to engineer your own compositor and DE on your own stack, then you should take the opportunity since that's a once in a lifetime thing (considering wayland KDE and GNOME have dominated the space for so long).

but I am skeptical about System76 dominating development rather than letting the community run things

Don't worry, they've already been accepting community contributions to COSMIC (such as gestures and window preview). They just have to work on finalizing the initial foundation of libcosmic and write documentation for it (but there are already non S76 COSMIC apps). They're also leveraging the Rust community's crates to build everything while also giving back to the community (like with cosmic-text text rendering which has become the de-facto standard on Rust). Iced is entirely community maintained and isn't even at its stable 1.0 release yet.

Rust rewrite of GTK

The issues they had with GNOME went far beyond the application toolkit. GNOME simply wouldn't implement swiftly (or at all) wayland protocols and desktop features that their (S76) clients and userbase wanted. COSMIC is exactly what you're asking here. They will have desktop extensions (and applet extensions), just not the ones GNOME have already.

They look like a mix of the awkward elements of Qt and Android.

I had that impression too. And when you're using it there's no animations or transitions between widgets. It's very much still in the pre-alpha stage right now (they even disabled light themes because theming wasn't working properly). I didn't like how far spaced apart some widgets were (like in COSMIC settings but that app isn't even near to be completed).

Even in these screenshots, I still far prefer the aesthetics of the Libadwaita apps. I wonder if there will be Adwaita themes for iced eventually. Not sure how well it would mesh with the iced layout though.

No one is beating GNOME on aesthetics no matter how hard you try lol, they cracked the code pretty much for the most appealing applications. But I think COSMIC's support for advanced theming that you can do on the fly will distinguish it aesthetically from KDE and GNOME apps (which have no such 1st class feature, yet. I know KDE is working on accent theming for 6.1). You can also change icon themes easily and Qt theming is still in the works so there's an effort to make the desktop integrate well together no matter the app.