But that's the thing - with Lukaku out, United's reliance on a system that plays one way around one player to make him work was exposed. Even Mourinho admitted as such - they quite literally had no Plan B because if Lukaku isn't there or doesn't turn up, United are blunted. He even said that in the event of having Lukaku out, they at least need Fellaini because they have to have one focal point to play to; their whole game revolves around that concept.
Whereas if their system was built around a fluid attacking unit, like Liverpool, City, Barcelona etc. etc. then you cope with one element being out because you play a varied way.
That's why I don't rate Lukaku as a footballer, because he requires others to make him better rather than contributing to make others better around him. It's a team game, especially at the elite level, and that's why Lukaku is now at a B-tier 'top' side not winning anything, instead of at the elite club that his goalscoring record would suggest he should be at on paper.