In order for avoidance to outweigh endurance, it would have to become reliable in some way (like the way that block capping worked in pre-MoP WoW). That's not possible in Rift, therefore it can't be worth more. Avoidance and effective health fulfill fundamentally different jobs. They can't be weighted or numerically compared. All you can do is look at the situations that kill you and determine what stats will help. And in the high burst, high healer output scenarios we see in Storm Legion, the answer is always effective health.