I think the concept of slow is relative here, for a no configuration start (from a fresh install) alacritty is slower by a factor of 4 https://news.ycombinator.com/item?id=40559084

However the absolute times are still probably not noticable unless you often cold-start terminals.

                     | Alacritty | Foot | Foot Client |
  Absolute time (ms) |    99.0   | 37.2 | 22.8        |