When was the last time you tried it? Atom works fine on dell computer with Intel duo core 2 from 7ish years ago.
[1] I know such a search is ridiculous, but both editors perform search-as-you-type, although atom does attempt to delay that if you type quickly enough. Anyway, it's just an example to demonstrate the speed difference.
The built in search is slow (for now), but they have been steadily making gains and use performance testing to measure progress.
Good news, it exists. If you know Go it's possible to see it sooner: http://limetext.org/