Earlier quoted context omitted.
the extension language, I'm guessing.
The second half of that line seemed to be alluding to something else. I'm not saying it's fast, but I've never encountered it's speed being a problem in practice.
Compare it with emacs in which I have far more plugins and it still starts fast as a clean install.
Anyway not a big problem eh. For me vimscript is the shitty part of vim.