Atom's speed has increased so much that I usually don't notice a lack of performance anymore. Startup time is one second flat and unless I'm opening huge DB dumps or have dozens of selections at the same time, it feels just like Sublime Text.
I have some programs that take (too) long to start up: Elite: Dangerous and Star Wars - the Old Republic. My web browsers also start up too slow, but opening a new tab is instant, and that's all I do, anyway.
I recently thought about the craziness of these applications based on web technologies, with a 15 MB download and sometimes sluggish performance. We had full GUI OS [the QNX demo-disk] that fit on a floppy in the 90s - surely we can fit an editor in less than 1MB today, and have it perform more things, ~1000 faster than in the 90s?
When I work or need to open many files, I leave the editor running and when I don't need to open many files, the occasional startup time of 1-2 seconds is more than acceptable for all the functionality it offers. If you open dozens of files and close the editor every time in between, that's really more of a PEBCAK issue.