Agreed, this is one of the common misconception of Gnome 3. Gnome 3 actually encourages keyboard driven workflow: "Ensure that every operation in your application that can be done with the mouse can also be done with the keyboard."[1].
They use 'big buttons' mostly for accessibility reasons.
Although I personally don't use Gnome 3 as DE because of lack of customizations, I agree to most of their Human Interface Guidelines[2].
1. https://developer.gnome.org/hig/stable/pointer-and-touch-inp...