Wayland supports it (and Chrome supports it very well) but GTK does not. I run my UI at 200% scaling because graphical Emacs uses GTK to draw text, and that text would be blurry if I ran at my preferred scaling factor of 150% or 175%.

This works with GTK for me at least. I've been using Gnome+Wayland with 150% scaling for almost 4 years now, and I haven't noticed any issues with GTK. Actually, my experience is essentially backwards from yours—anything Electron/Chromium-based needed a bunch of command-line flags to work properly up until a few months ago, whereas GTK apps always just worked without any issues.

If you're using a high-DPI monitor, you might not notice the blurriness. I use a standard 110-DPI monitor (at 200% scaling in Gnome) and I notice it when the scaling factor is not an integer.

Chrome can be quite blurry if Xwayland gets involved, but if configured to talk Wayland, the contents of Chrome's viewport is non-blurry at all scaling factors except for PNGs, JPGs, etc. For a long time, when run at a fractional scaling factor under Gnome (and configured to talk Wayland) the only part of Hacker News that was blurry was the "Y" logo in the top left corner, then about 2 years ago, that logo's PNG file was replaced with an SVG file and the final bit of blurriness on HN went away.

Compared to the contents of a browser's viewport, Emacs and the apps that come with Gnome are visually simple, so it took me a year or 2 to notice (even on a standard 110-DPI monitor used at 150% and 175% scaling) any blurriness in those apps since the app I'm most conditioned to notice blurriness is my browser, and again Chrome's viewport is resolution independent except when rendering certain image formats -- text is always non-blurry.

GTK uses Pango/Harfbuzz and some other components to draw text, all of which are widely used in other Linux GUI stacks. GTK/GDK do not draw text themselves, so your complaints are not with them directly.