Someone in this thread mentioned that in case of GTK all backends are loaded at once and cannot be separated (unlike Qt).
Yes. And then you argued with my post without reading it.
I have no reason to believe the Wayland backend of GTK cannot be broken out into a dynamically loadable library, as in Qt. That just hasn't been done yet, so at the packaging level, it can't be split up. I've opened a bug requesting it in response to the "won't fix" this article is about: https://bugzilla.gnome.org/show_bug.cgi?id=690381