In case it helps anyone, you can fix blurry X11 apps in GNOME by disabling fractional scaling like this:

  settings set org.gnome.mutter experimental-features "[]"

Indeed it isn't the best experience and hopefully XWayland gets some better defaults, but fractional scaling cannot work well unless apps support it natively since text needs to be rendered at the correct DPI or exact 2x/3x multiples.