This is just about too evil against warriors in PvP because it'll take 6 seconds for them to use their signet and they'll be getting double damage to them for 6 seconds. Also, this makes it difficult to use res signet.
Rust is great as part of a hex team, now that it got its recharge buffed its a essential skill for any water ele.
No
in a gvg situation or even hoh for that mater running rust is not the greatest idea in the world, let alone essential.
most of the time water ele builds run something like this,
1.shard storm
2.ice spikes
3.deep freeze
4.blurred vision
5.ether prodigy
6.heal other
7.heal party
8.res sig
in pve rustdoes have some uses like ettin farming with eles but other than that it hovers over being completely pointless