All WL specs are good (Demo is okay) but you have to like three button pve rota.
Its hard to say for the new expansion. Spamable cc and enough dmg will always be okay.
Legion pvp is annoying overall and you cant outplay other players anymore.
They hit their biggest offensive cd -> you hit your biggest defensive cd. Everyone can deal damage because its too simple.
There are also plenty of other threads about comebacks: