GNOME is primarily about making Free Software that is highly accessible. The desktop and GTK toolkit both predate OSX, so I'm not really sure what the purpose of the comparison is.
This criticism is for the more recent versions of GTK.
Killing theming and removing features when they do not have a serviceable usable alternative does not make it more "accessible", it is just the standard "we know it better because we study the behavior of a large group of users" excuse that they give to treat it everyone by the lowest common denominator - just like Apple.
Yeah, that much I generally agree with. Many of the 'opinionated' decisions that came with GTK4 are either regressions or strange and inflexible.
That being said, I will shamefully echo the words of the GNOME maintainers; their goal was not to "kill theming". They wanted to stop distros from shipping themes by default, which was arguably just as deranged but at least somewhat understandable. Nowadays we have stuff like Gradience too, which lets you theme LibAdwaita apps. You're still forced to use the ugly old Adwaita buttons, though.
So... make of it as you will. I left GNOME completely after the GNOME 40 update, I sympathize with people who hate the current desktop. The toolkit itself is "fine" in my unprofessional developer opinion.
Killing theming and removing features when they do not have a serviceable usable alternative does not make it more "accessible", it is just the standard "we know it better because we study the behavior of a large group of users" excuse that they give to treat it everyone by the lowest common denominator - just like Apple.