Your argument gives you a bias to look at things negatively. So in your mind, Lukaku was slow...but Fellaini still has to run back and make the block. You know? Defenders should be in that position, but they were no where. - they would have been closer to making a challenge so ultimately it was a good decision. But people have a bias.
We have to think about the group dymanic too. Would you sell one of Martials best mates?
In turn, that might disappoint the dressing room. We've a good team spirit at the moment - despite everything. You can't have a team full of Martials.
Fellaini isn't the reason we've flopped this season or any of the seasons. If we win the FA Cup it will bring tremendous confidence to the team.