Waqar Younis is probably responsible for Naseem's shortened runup, which has taken away his best traits as a bowler. When he came with a longer runup, he'd get naturally more pace and with that pace would come a decent height for bounce, which he was used to all his life.
At this pace, he doesn't get the same bounce, and so he has to adjust almost every aspect of his bowling, which is too much for a 17 year old. Waqar Younis is gone now, so Naseem needs to go back to his old runup because Waqar has not added any skillset to the current bowlers. No seam movement, no well-directed bouncers, no swing skills either.
All I've seen Waqar Younis do was help Shaheen and Haris Rauf nail the yorkers and act as if he'd just saved Pakistan Cricket, but if someone disagrees, feel free to tell me what else he has done with our bowlers.