We've waited a long time for someone to actually have a good average and a decent strike rate at 7. And finally we have that in Imad, 36 and SR 99 is very good. At times yes he doesn't look like a proper batsman, but he consistently makes runs lower down and bolsters our total.
Imad's bowling in ODIs is OK, not terrible. On some days he looks innocuous. An average of 36 with the ball at an economy of 4.6. He's generally good at keeping runs down though, you don't expect him to go for much. Arguably his bowling may be worse as a result for so many options in ODIs he doesn't get to fit in his quota most games. In ODIs his main job is with the bat. In T20s, 7 is quite low so he often won't get much time to bat, his main job is with the ball.
Fahim could be better, but with the ball while alright, did look like he'd be hit more than imad. And while we don't necessarily have a standout spinner (Shadab is still very new), we have four pacers that most will agree are better than fahim with the ball.
Fahim with the bat could do well, but it's a bit debatable. He only averages 15 and 10 in list A and T20s respectively. Perhaps he should be given a chance to show he can do well with the bat in domestic limited overs first.
You can take a risk with Fahim, but I don't see it likely he'd outperform Imad, especially with the ball. And Imad definitely is an asset at the moment. It seems a bit strange to base it around one knock which many are doing, that too a in a warm up against a weak Bangladesh bowling attack.