I think, problem for PAK is the UAE venue - the wicket there in recent years is tailor made for 35 overs of spin. It's not feasible to accommodate 2 medium pacers behind Amir & Hasan in UAE - even bginging one is challenge. This is one of the main reasons for such prolonged stardom of MoHa & Afridi.
In 80s & 90s, PAK played lot more matches in AUS/UK & the home wickets had something for medium pacers, at least it swings in Punjab & reverse swings at Karachi, while old UAE wicket had a mirror like shine that helped movement. That was the main reason PAK Captains tried so many medium pace all rounders from Shahid Mahboob to Yasir Arafat - that privilege now is going to MoHa, Malik, Imad, Nawaz ...and this is one of the main reason for this 8/9th rank - PAK as a team, it's core strength lies in attacking cricket - this 35 over spin strategy in UAE didn't win series against SAF, NZ, AUS & ENG. Shukar hai, IND doesn't play PAK & PCB don't invite BD in UAE - otherwise, on those UAE wickets, it'll end in embarrassment.
On a better surface, ideally both Yamin & Fahim should back 3 men front line attack of Amir, Hasan & Shadab (ideally the best leggi available, purely on bowling merit only) - Just like Razzak & Mahmood backed 3 men attack of Wasim, Shoaib/Waquar & Saq. Imad is a decent utility cricketer, but unfortunately, his bowling is going to work only on those typical UAE wickets - dead slow & low. He should be part of T20, but not the longer formats.