And since precession on a gyro is always 90 degrees later than where the force is applied, the fact that different helicopter rotor systems have phase lag angles of less than and more than 90 degrees rather puts the whole 'precession in a rotor system' argument to bed, once and for all. The precession argument is for people who don't understand flapping.
TGZ - in a still air hover, all the blades experience the same speed of airflow ie that of the rotation of the blades. Now add 20 kts from the front. The blades over the nose and the tail will have the same speed of airflow since they are crosswind but the blade at 3 o'clock will have an extra 20 kts and the blade at 9 o'clock will have 20 kts less.
Now start with the blade at the tail and move it towards the nose - it starts to see an increase in speed as soon as it moves and begins to flap up, slowly to start with but increasing as the speed increases (lift increases as the square of the speed) until, at the 3 o'clock position, it has maximum speed and therefore maximum flapping up. Even though the speed reduces between the 3 and 12 o'clock, the blade doesn't flap down, it reduces its rate of flapping up until it reaches its high position at 12 o'clock.
Now from 12 to 6 o'clock on the retreating side, the process is reversed.
This is basic flapping to equality and highlights that 90 degrees after the maximum effect (adding 20 kts in the 3 o'clock), the blade reaches its high point. So if we want to make the blade high or low, we must rig the controls so that we input the required pitch change 90 degrees before hand. This is achieved by putting the hydraulic jacks 90 degrees out ie fore and aft jack in the 3 or 9 o'clock position - or by having the pitch change rod on the blade mounted ahead of the blades feathering axis - or more usually by a combination of the two.
Now all rotor systems are not equal and are not gyros so, because of the rotor head design and the weight and inertia of the blades, phase lag on some helicopters is not 90 degrees (your instructor has quoted 78 for the 300) and the rigging of the controls and pitch change arms will reflect this so that any desired blade position is initiated by changing the pitch 78 degrees earlier. The reason for doing this is so that forward cyclic in the cockpit results in forward disc tilt (apparently Igor Sikorsky's early model didn't have this yet he still managed to fly it).
Phase lag changes with density altitude as the Lock number changes (blade inertia v aerodynamic damping) which also doesn't happen on a gyro for those doubting thomases.
Hope this helps TGZ, if not - do a search on PPrune as this has been debated extensively before.