7k backstab is high in pvp. You may have to build more tankiness. No one can go full zerg. Killing thief is not easy but you can read its game. A thief can't fight indefinitely. When they start do dodge after the first burst it's at this moment that they have no or less initiative. So you can try to kill them but you have to know that you enter the thief game. If you don't chase, you take advantage while you get back your cd's and increasing the gap betwin the opponent and you. That will cost ini to fill this gap so less damage if the thief is chasing.Playing a thief can teach you how they stealth and for how long with which spell.About builds, don't chase daredevil who run the dodgedash. The counterpart of this "unkillable" build is that it can't kill anything and they are weak in 1v1 unless you take the cc when you try to heal up you won't die. The thief will reset 'till that moment happen (d/p one). For dead eye, you can't do anything if they one shot you but they have a low mobility and stealth don't mean immunity. Just AA where they dodge, aoe and they die. Deadeye have low def, it repose only on stealh. Thieves aren't the problem since backstab have no damage in pvp and have a 1sec cd