Agreed. Atom seems intended to be a drop-in replacement for Sublime. I tried it out again a week or so ago and found it almost at parity. The speed issue mentioned here is one of the biggest reasons I went back to the closed-source Sublime.
The speed, and the text rendering for me. Sublime renders the fonts I use better, and it supports bitmap fonts, which I am still fond of.
I don't use Atom so I can't compare directly, but from those comments even Xcode sounds faster.