Is not correct.
Let's looks at the report. The first thing that stands out as a glaring anomaly in the chart you posted is the fact a 4 bladed propellers appears to be more efficient than a 3 bladed propeller.
This violates a basic principle, sort of like all those people who want to claim their higher wing loaded aircraft can outturn a lower wing loaded airplane. Sounds nice but is not going to happen.
That principle is the fewer blades, the higher the efficiency.
The NACA is not claiming a 4 bladed propeller is more efficient. In fact, they quite notably point out several times in the report that none of the data is corrected for wind tunnel installation.
In English, it is not good for specific comparison and they plainly state that in the conclusions. They just hung the propellers and went with it to get an idea of the general trends.
The NACA conclusion are the ONLY thing that can drawn from this report.
You calculated for an advance ratio of 2.78.
The 4 bladed propeller produces NO THRUST for most of the power loading conditions at J = 2.78.
When the polar line ends,
the blade is stalled!!!
Your theory is not based on facts. It would be a fundamental error to toss aside convention of n = ~.85 for it.
