as far as I am concerned I have never witnessed such difference
Well, I have and so have many others. In my last job where some of the legs were well over 200nm it was quite common to see a 2 or 3 min split between times on the ND and in the FMS. Particularly where you might be entering/leaving a jetstream between those 2 waypoints.
Do you think we should all write to Airbus?