I switched from sublime to Atom maybe 2 years ago. I'm completely happy with the speed. I see no disturbing lags and it works/looks the same on every platform. There is a great extension system and I can develop my own extension quickly if I ever needed to. I believe for the developers it was much more productive to create it with web technology and therefor I don't see any reason why it shouldn't be done like that. I guess there are people that need much faster this or that, and as low memory footprint as possible, but it is not an average user/developer. I believe for most of us these editors work well