Playing with a lock on my team and also fighting against locks I have never seen a class just die through their primary major long cooldown defensive as much as I see locks do. Locks do not feel very durable this season from my pov.
For example if a ww is max bursting on your lock who walls at full hp with like a commet storm combo from a frost mage and you get incapped roar into full clone your warlock is 100% dead there if he does not overlap other defensives like port or hs.
A 3 minute cooldown defensive should be a garuntee save.