why is Attack Speed important for Crit ?

attack speed is almost always welcome with attack builds, crit or no crit. Speed does help bring around more crits per sec, in that sense it has a similar value to crit chance.

However with bows a Harbinger is usually the crit bow of choice, its not the fastest bow, for phys daggers a Platinum Kriss would be my weapon of choice, again a slow weapon. I would want high attack speed rolls on both though to bring them back to somewhere that doesnt feel sluggish.