2 or 3 attackers were not necessary to send a violent message to IK and PTI, only a trained sniper from any of the Institution under Ministry of Defence or Ministry of Interior could have injured IK more seriously (or even killed) without even get noticed by anyone.
For example We already have witnessed the video footage of Benazir Murder were exist of bullet from the backside of head of Benazir is visible, that shooter (probably a sniper) who actually fired that bullet which killed the BB was not traced by any agency ever.
So on the basis of details now coming out it seems on paper there was a perfect plan with multiple options and attack possibilities; all the elements of success like surprise, deception, distraction, influence on Police and local handlers etc. etc. were there, but somehow they failed at the execution stage, because of failed execution IK survived this attempt on his life.