I don't agree. Reading Gnome designers' blogs makes it pretty clear that they strongly believe in these decisions as the best UX. Looking around Gnome reddit there's also plenty of people who like this minimalism and think it's actually superior [2].
That's not to say that the designers are not supportive of the existence of extensions. They clearly do, that's why they make a nice Extensions app in the first place. But they never say "yeah, we made it as barebones as possible to make it easy for extensions". They explain why it's better for users not to have a minimize button on windows [1], or why they've removed the systray to avoid confusion and so on [0].
That's not to say that the designers are not supportive of the existence of extensions. They clearly do, that's why they make a nice Extensions app in the first place. But they never say "yeah, we made it as barebones as possible to make it easy for extensions". They explain why it's better for users not to have a minimize button on windows [1], or why they've removed the systray to avoid confusion and so on [0].
[0] https://blogs.gnome.org/aday/2017/08/31/status-icons-and-gno...
[1] https://afaikblog.wordpress.com/2011/03/01/where-did-the-but...
[2] https://www.reddit.com/r/linuxquestions/comments/11bhxa7/com...