Only England and to a certain extent, Bangladesh, have a genuine all-rounder. Pakistan's biggest problem is the lack of experience of their batsmen. Shadab and Faheem are decent options to come in at number 7 and 8. If you're relying on Shadab and Faheem to win a game with the bat, when the top order has completely collapsed, you're watching the wrong sport.
Every good team has at least one-all rounder that's better than both Shadab and Fahim in either batting or bowling.
India - Pandya's a better bat than Shabad and Fahim and a better bowler than Fahim.
Aus - Mitch Marsh - a much better batsman than both Fahim and Shadab. WC experience. Better bowler than Fahim. Even Pat Cummin's record as an AR is much better than Fahim and Shadab's.
Eng - Stokes, Moeen, Woakes all of them are better all-rounders
Ban - Shakib is obviously the best all-rounder in the world right now
SA - Morris hasn't been playing much lately but he's a genuine all-rounder and again, better
The only two teams today who don't have a genuine LOI all-rounder are Pak and NZ. Luckily, NZ can get away by having players like Guptill, Taylor, Boult, Southee and Santer. Pak does not have that kind of experience or quality in the rest of their lineup right now. They need to find a better AR.
Either of Shadab or Faheem should play depending on conditions. I have high hopes from Shadab and I think he should get the nod ahead of Faheem most times.
Pak's problems are actually quite similar to India's. Even that team is currently short of one AR, even with Pandya in the XI. That's why someone like Kedhar Jhadav has to be accommodated into the squad. Because we don't have much choice. Just like India, Pak's batting also has genuine tailenders starting from number 9, which is one position too high. That is why it is critical for both India and Pakistan to find not one, but two proper ARs to slot in at numbers 7 and 8 before the WC.