Human seem to have very different tolerances for latency. I've had someone call me over to their desk to show that Eclipse could be fast, and what they described as 'responsive' I find 'hair tearingly laggy'. He's not wrong, and I'm not right, we just have different expectations.
When it comes to typing lag specifically, anything more than "imperceptible" is too much for me, and I think most people would agree. Having said that, I have never observed any kind of typing lag from Atom.
Javascript
More like DOM
So JavaScript is the reason different Atom users have different levels of lag? You realise they're all using JavaScript right? It isn't optional on Atom.