I don't know when the perf improved, but it definitely has recently. In the past month I downloaded Atom on OS X (for the third time) to see if the perf had improved and I was impressed! I added a huge project's folder and indexing was done insanely fast (iirc less than 30 seconds). I don't really have a need for Atom at the moment since Sublime Text exists, but I might recommend it for new programmers since it's free + hackable.