Why you comparing a pve ranger with pvp dk, it doesn't make sense.
Rangers can already hit 800-1k dmg to a death knight same as bd.
Yes it would be a great buff for wardens but life steal will nullify the dmg reflection because like you said, 30% dmg reflection = low resilience which means you can use a life steal + dmg critical set.
Do you still think it's bad? Just want to hear your opinion
Ps: what class are you playing