Exactly- the prop is essentially a wing, and is most efficient at a particular angle of attack. The blade angle to achieve this will vary with airspeed.
COULD be that the pay-off is less than with a piston (or turbine for that matter) and a cruise-optimised prop may be sufficient in most cases as, as you say, there will still be maximum torque available at lower speeds, and thus not worth the cost/weight/complexity.