crit is a weak stat which is to risky on draven when u need to secure kills, going for full lethality especially in patch 7.2 when it is so strong. The lack of attack speed is made up through the 2 auto for a kill late game. You also get plenty of lifesteal due to the big damage with the massive lethality. On top of this in late game teamfights his w gives him plenty of ms and attack speed.

the reason that both edge of night and merc scim are built is because edge of night isnt just an mr item when trying to survive vs an assassin. it can block rengar and khazix q giving him a lot more survivability.