When you are in position, who care how heavy the backspin is, just loop it however you want. A sudden fast deep push usually means you are out of position, and you have to mostly use arm and wrist. Still, you have two ways to loop.
1. Loop drive. The key is to overcome your fear, counter your intuition to brush up, instead, put more power on forward motion. That is, quickly engage and pin the ball on the rubber with a powerful forward swing, and then a brush up a little to lift it. You need more power in forward than your normal loop drive.
2. High loop. Twist your wrist as soon as you hit the ball and move your arm more upward than forward.
Basically, you counter the backspin either with speed (loop drive) or with spin(high loop). Even if you are out of position, your arm and wrist should have plenty power to return it. If you used a lot of power, but the ball still went in the net, you either did not move forward enough, or did not use wrist enough.