I love this game. Hands down the best-polished gamified typing test I've come across. The only typing test I've seen that's better is the one from ManPower, and maybe the Programmer's Typing Tutor (https://typing.io/). But those are more focused on applied typing.
Regarding the typing too fast for the game to keep up with:
> Yeah that's an issue with the WebGL version I've tried to solve, but I haven't been able to find out why yet.
Just a shot in the dark, but perhaps you need to increase the input framerate? Browser-based games often automatically decrease the visual framerate, due to resource limitations, and if people are missing (or swapping) letters, it could be because they type them in the same frame. So manually increasing that, or putting it in the physics ticks instead of the graphics ticks, may fix that issue.
The only real complaint I have is that I can't use the backspace to turn an incorrect word into a correct word. So I have a 75 WPM / 100% Accuracy on other testing sites, but I can only get up to 55 WPM / 85% Accuracy on this one. But this feels so much better because there are cute cats cheering me on!