Amir was criticized for precisely doing the same in PSL. He was very economical with not many wickets. Bowling at the death is actually favorable for Mustafiz. He can't swing the ball much and will not be allowed to open the bowling. He should be picking up tailenders and sloggers but he's averaging about a wicket a game. Is that his role or is he not the 5fer bowler anymore? I maintain my position that the batsmen who've played him before are able to read his cutters and are also playing him cautiously. He can pick wickets only if the opposition is trying to slog. That has been the pattern.
You do realize that the reason why Mustafiz isn't getting too many wickets is because batsman are trying not to open up against him? These are not minefields where any bowler can bag 3-fers 4-fers with conventional bowling.
About him getting wickets only when batsman attack him. Well isn't that the case with all bowlers bowling in the middle and death overs? And some of his dismissals were from yorkers where the batsman couldn't even put bat on ball.
Also, Jadeja and Raina have played plenty of Mustafiz, yet they couldn't do much about Mustafiz.
And as far as his roles are concerned, he has a different role for SRH as opposed to BD team. We have some decent death bowling options like Al Amin, Taskin and Shakib. SRH has only Bhuvi to partner him, ofcourse Mustafiz will have to do the bulk of the bowling in the death. If you are bowling in the death and giving away less than 6 runs an over then you are winning more matches than a random bowler who takes two-three wickets in the death but gives away 20-30 runs.
You play according to the match situation and what your pre-defined role is.
So in his 4 matches he has the folllowing stats
26-2 in 4 overs when the opposition socred 229
28-1 in 4 overs, not a great performances, didn't get support either from the batsman
32-1 in 4 overs, a good number of the runs came from misfields. Regardless, went for 10 runs in his last 2 overs.
19-1 in 4 overs, 3 overs were bowled in the death and 1 in the middle of the powerplay with Baz and Raina.
However, if you put on your hatred glasses you will try to scrutinize him.
Even if he takes 4 wickets but gives away 35 runs you will say the exact opposite: He took wickets but gave away lot of runs, hence his spell was useless.