Define Hella fast.
If you want 16ms text rendering (~60 Hz) you pretty much need a GPU today. If you want 8ms (120Hz) text rendering, there is just no CPU that can handle it today with an OS running next to your text editor doing other stuff.
The whole point of Xi was being able to edit huge files (Tb size) on 8k displays at over 120 Hz, and being able to resize the screen and scroll, resize text, with great fonts, without any delay or sluggishness.
Xi delivered in some of those things, and druid delivers on some of the others.
But essentially, there is no system today where you press a key and that key appears on your screen in less than 8ms. Xi achieves ~16ms on the right platforms - not the fastest but much faster than most text editors.
The idea behind Xi was to preserve that as the editor got more features, like syntax highlightning, and it did.