Yeah I'm with her, a cooldown doesn't have 100% uptime and should not be considered the same as something that's just part of your rotation for the same reason as Brutal Shell, Storms Path, and Souleater aren't treated as actual healing cooldowns.
But the other side of the problem is that with barrier-style tanking, any damage that happens stays. Barriers are basically just an HP increase but your current HP always stay the same. This is what is really making DRK feel weak. Other tanks don't need help getting their HP up, DRK does, no matter how much damage it blocks.