It's just not about the max damage of a slower weapon. For crits, it is about having a high max damage AS WELL as a smaller damage spread. A slow weapon with a big damage spread have a bigger pool for the crit random damage number roll generator to determine whether a critical hit uses just the MaxDmg+1 critical hit or uses the CritMultiplier x Damage roll for the critical hit; it takes whichever is higher according to the damage roll. Kall submitted a very informative post about this in the
New old question thread.
Haste and attack speed in combination are awesome to bring down the weapon delay of those slower weapons so you have more opportunities at a possible chance to trigger a critical hit; also, slower delay means ya will have more opportunities at a possible chance trigger double auto attacks that can possibly critically hit as well
Haste items give tremendously more attack speed; I think this is why it was implemetned that Haste mod items do not stack. The attack speed attribute comes in small increments on a per item basis and this is why I think it was allowed to stack.