I tend to agree multi step isboxer keymaps specially with "Do not progress to the next step for X time" is indeed the same as a delay
(and yes key up vs key down is very convenient but...)

I guess the general idea is don't mash 1 key that does a gazillion things while almost afk - be there to play the game and control your toons

(in the specific case though, I think having 1 key for assist and 1 key for iwt is fine; I don't think there is much delay in the default wizard for isboxer but it ends up doing those 2 each spell cast (assist+cast) in 1 key press (and release))