Even though the coupler will rotate the magneto slightly to improved the spark....

....the prop has to be pulled through in a fast, positive hand propping motion to
generate a spark, or be turning with the electric starter to produce a spark.

The safety feature of this built in factor is so the magneto will not fire if it is
rotated slightly by accident, and also the safety factor of not firing in an advanced
timing mode....therefore protecting the starter and flywheel on the engine from
damage resulting from a kick back.

The engine will still not fire if you lean on the prop, or move it slowly by hand....

....this is balogna.

FBD.