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.

Khan can destroy/disrupt fernando shield. Keep shooting Fernando forcing him to throw out his shield then use commanders grab to disrupt it. Even if fernando has max resilient doesnt mean he can escape stun. Equipt Vortex grip for better result