Whe an engine manufacturer does the dynamometer test for a motorcycle, he does not state what size of wheel you have to use with it.
Why do the great Tohatsu not state the engine power against crankshaft rpm? Surely they can find a dynamometer somewhere. That talk about a 2/3 variation in the power output is garbage... notice it is always derated, not uprated. So, a 6 hp motor can drop to 4 hp, but never 8 hp.
They don't have to mention props.
Just publish the power curve.... power with engine rpm.
Chosing the prop would be the owner's problem.
Measuring a bollard pull is not much use. Not too many people tie their boat to the dock, in gear, with the motor running. It frightens the fish.