I kind of agree. If you are getting the same amount of thrust, with a less efficient prop, then I agree, the engine is must be doing more work. However, if you improve the prop's efficiency, and it is the only change you make, you may get more thrust out, without adding much, or any load on the engine.

I do believe that different engines will find better or worse performance with the same prop though. This is due to the differences in the engine's torque curves; i.e., where they make their best power, because just like engines, different props will be more or less efficient at different RPM. This is why there is no "one right Prop" or engine for any plane.

Jack