To counter Khan shield without buying wrecker, go to the highest platform and shoot above him. He will resort retreat. There is very rare chance if you manage to shoot his feet just like Vivian. Only snipers can do it but very rare.
If enemy Talus isn't using Faustian Bargain legendary, after finding his rune, it's guaranteed he's going to teleport here after a couple of seconds. Use it to your advantage, when confronting him.
Your shadow travel can make you immune to everything. Use it to cancel ultimates and abilities, or use it in sticky situations. (I recommend using veil since it can make you go into shadow travel faster.)
Try to separate him from his turrets and wait out his shield because of the short duration of the shield. Do not let him be first on point and set up turrets.