The author calls this out and tries to brush it off with FPS figures,

> The current version of the base engine renders extremely fast, faster than most would think a garbage collected language could go. In my testing a release mode build of a game in Unity with nothing but a black background and a cube runs at about 1,600 FPS.

But straight-up FPS is generally not the main concern with GC in a game engine, it's GC pausing which can make an otherwise smooth game feel almost unplayable. I don't know anything about Go so maybe this is less of a concern in that language?