Is Deceleration spell useful?

[Piter]

If mob have 1actions and attacking once a 60second then with 2actions he will attack once to 30second, 4act=15sec, 8act=7.5s... If animation of attack is longer than this time, then slow/speed have no differences.
From other side if mob can attack once to one second with 15action (and animation not slowing this) then with 8action it will be 2second, 4act=4sec, 2act=8sec, 1act=16sec, slower is impossible.
melee you seen little differences because weapon have small actions and short animation
archer no difference because they have small actions and long animation
spellcaster have bigger difference because they need more actions and animation is starting after raising hand