As has been stated, this is over old ground...... As has been stated the 3 peaks is not just about the distance, it is the terrain, the climbs, and the descents - as well as the weather conditions. I am not sure of the reasons for the reservations of the leader, clearly he has reservations and I would think that it is important for you to trust his judgment. After all, would you trust him to lead/guide/take you if he was irresponsible putting anyone at risk?