I use emacs every day, with a minimal config, and would never describe it as snappy. The entire thing is single threaded so the UI locks up at the slightest provocation, like for example when firing network requests whilst packages are updating.
Emacs can run external processes asynchronously. It is true that Emacs locks up while updating packages but it is actually not while downloading or unpacking them! It locks up while byte-compiling them. :)
I remember I looked into a lockup I was experiencing (this was a few years a ago so I forget the mode). Turns out emacs was writing to disk every so often and this was noticeably causing stutters in the main thread.
