In response to the OP it's Mourinho's decision how he see's fit, how the feck should anyone really 'know' as definitive as he should or should not hire someone. However as a forum for opinions, going away from the question to a broader sense we have performed better attacking wise than Van Gaal sides or Moyes sides in my opnion. I trust whatever Mourinho brings to this issue from his track record.
With regards to our play:
Ibra despite scoring 28 goals doesn't help the other attackers in the sense of his his lack of movement, that's not to say Ibra should be out of the team full stop. Clearly he's contributed to our team in a big way to get goals, but the focus is to much on him, he's missed the most clear chances this season, he's a good finisher but for me over the course of his carear I would never have said he is close to being one of the best finishers in the game, he is much more rounded than being a pure finisher.
With Ibra playing centrally we don't get to see some of the positives of last season with Martial and Rashford playing more centrally being dynamic and causing more panic to the centre of the pitch. In our team it feel sometimes thier pace is just ineffective when playing wide, or sometimes deep wide.
Width. There is a lack of it in our team, I almost envy when Guardiola instructs his players sometimes to keep to the touchline which also creates space centrally. Perhaps im missing more important issues such as the timing of a full back overlapping on the wing to provide an option to drag defenders away and pull he opposition all over.
Crossing. Our most effective crosses are back post when Zlatan/Felleini are there, or getting to the byline and cutting it to generally a runner from midfield. Zlatan is often wondering too deep as he plays in a false 9 a lot of the time and we just have a lack of numbers in the box. Iv seen too few times this season where we finally manage to get a excellent low cross into the 6 yard box but no-one there gambling to get onto the end of it, to be fair to Mata he does this better than the rest. Again I believe when we do get into these positions we encounter so many blocked shots because were doing these actions to slow to catch out the opposition, it's a case of split seconds for our attacking play when the delivery should be more often than not, first time ball rather than for example Valencia getting superbly into a wide positon and then hesitating to long, pass, blocked shot/defenders having time to position themselves correctly. We need to be much quicker and decisive in these positions. Maybe im asking to much there I don't know but look at last nights goal ( v Anderlecht, Valencia first time cross) or West brom away (Zlatan goal from first time Lingard cross) These are quick transition periods and defenders are going to struggle more to block and havnt got the time to camp and sit deep. Perhaps thats another subject.