A fan producing thrust is obviously providing a forward lifting force towards the front of the engine (+ thrust) while a fan being spun by the relative airflow is now providing a fan force towards the rear of the engine due to a lift force on the rear side of each blade (-thrust)
Windmill drag is obviously significant enough that aircraft now use thrust on descent to reduce drag. While I remember the A330 having it from what I imagine was service entry, you’d descend with an EPR of 1.0 or so, the 747 only got thrust on descent with the NGFMC and the introduction of the 747-8 ie circa 45 years late.
So we’re back to the beginning is the interference drag reduced more or less than the negative thrust component caused by a windmilling engine?
I guess you could plot windmill N1 / EPR vs airspeed and see if it’s a direct correlation or find a aerodynamicist.
I’m going with windmilling has more total drag or penalty than a locked fan.
Logs added to fire.....