Xfce is a pretty complete desktop experience, assuming you think Windows 7 was about where it peaked. You don't need to use the defaults.

Xfce relies on GTK, so it would seem subject to the whims of the Gnome team in a lot of ways. Do you know of any plans to wrest control of GTK away or fork it?

I don't think XFCE intends to switch to GTK4, and if they do then it will probably be towards the end of the update cycle.

That's not the problem. The problem is that any Flatpak I download also comes with several gigabytes of GNOME runtime dependencies, which is absurd and shouldn't be treated as "the new normal" of software distribution. Running to alternative DEs doesn't solve the problem.

That was already the normal long before flatpak. Installing the same packages with your distro package manager will also install the same several gigabytes. The number you see in flatpak might be an illusion though, the real amount of space taken up on disk is less: https://blogs.gnome.org/wjjt/2021/11/24/on-flatpak-disk-usag...

So flatpak may actually be a solution to the problem that you don't realize. It can only cause a big issue if you have a lot of old software that never updates the runtime.