The old Legacy Nats will **get you one shot or miss 1/3 of your dexterity**, is the correct thing. That bonus is not even great in PTR 2.0.1, let alone at lvl 70, Id take the new nat in a heart beat even if they had the same stats, unending Rain of vengeance > discipline regen that you dont really need (gear is flooded with + discipline and nobody even use shadow power anymore, if you had not noticed yet).
Im not even sporting any of the passives that regen discipline and i have too much for what i can do with it on the beta, i dont get what OP you could get from that set, aside from terrible stats.
It could work OK with Mystic re-rolling some stats and maybe that -1 to set items ring but I agree that it definitely won't be OP, but I'm still gona save a set. Would be nice in PvP, just saying...