On my laptop this terminal is not very fast. A cached 'find /' runs in 11 seconds on an xterm, 17 seconds on maximized alacrity when it's on screen, 25 seconds on alacritty if it's off-screen, and 44 seconds on a 80x24 alacritty.
I don't know why it's slower when you make the window smaller, or when it's not being displayed. I expect the answer is "some kind of OpenGL bullshit" but beyond that...
gnome-terminal takes about 5 minutes to do this, but it has unlimited scrollback and as far as I can see alacritty has no scrollback whatsoever.