Not true. What really does the job is the aerodynamic flow of the expanding gasses across the turbine, not the heat itself. The exhaust gets cooler as it exits the turbine in the same way that refrigerant gets cold as it exits the expansion orifice, rapid expansion. Thats what confuses people into thinking that the exhaust heat is doing the work.

Think of a wind farm, they don't work by heat but by the flow of air across the blades.

Thats how VNT/VGT turbos work, they increase the potential energy of the exhaust by increasing its velocity and expansion ratio across the turbine.

Back pressure is a natural result of gasses slowing as it contacts the working surface (turbine).