That's right Redflyin, a jet aircraft only has a critical engine whilst on the ground, for the reasons you just mentioned. When airborne there's no additional yaw due to weather cock as there is on the ground.
Instead of saying a multi prop's critical engine is always the left side, I'd say's it's always the outbord engine who's prop is going down closest to the fuselage (fpr p-factor like you mentioned).....then it covers you incase the prop rotates a different way.