It is a common misunderstanding that all C programs are fast by default. In reality that's not the case. It takes hell a lot of time and resource to get that right. C programs just compile blazing fast. D compiles even faster.
I never use GNOME but I decided to try it to test pop shell awhile back. This was shortly before 1.0 of pop shell so it could have changed. Not trying to disparage it, just sharing my experience as an i3 user. It feels so so slow because of animations.
I googled how to get rid of animations because it wasn't in the GUI settings. Animations were removed, but a delay remained with any tiling movements where an animation would have been. Not sure if this is a limitation of GNOME or a bug in pop shell, but it wasn't going to work for me. It would be really hard to give up the snappiness.
Yes, as is Pop Shell implemented on top of Gnome (mentioned in another comment).
You can tell they've made some questionable decisions when you try to use Gnome on very weak hardware.
On an old dual-core Celeron w/ 2GB memory I found it unusable. KDE—which, when I first started using Linux desktops on machines less than 1/4 that powerful, was noticeably heavier than Gnome—was a little slow but basically fine.
To my eyes gnome also drops frames like crazy (like, even for Linux, which is a pretty jittery environment to begin with) even on excellent hardware—not sure, but I think it's a reasonable guess that's also a symptom of sprinkling a scripting language all over the system without incredible levels of discipline to make sure it's never in the way of anything important.
So is GNOME as far as I know.