Paul:
...Chieftan has identical engines. Another version, the CR, has engines which counter rotate. Now on the Chieftan the left engine is the critical one and on the CR there is no critical engine. The only thing that changes with counter rotation is P factor...
You still overlook torque.
On the critical engine. the left, torque tends to counteract the offset thrust, making it easier to fly than with the right only, where the torque and offset thrust effects add.
With the CR version the torque and offset thrust are counteractive on both engines.
With either version, in a dive, VMC still holds. And in that dive the airflow into the props is as close as axial as you can get it making P-factor absent by definition. And you still can't hold yaw at full throttle until your speed comes back up. Torque and offset thrust, yes. P-factor, a resounding no.
Bill.