Let us be blunt about this. This is a load of crap. Mourinho stuck by Lukaku, completely, which meant consistently playing him for the 90 mins for the majority of the matches until Mourinho was sacked. 16 PL matches he played, he started 12 of them and played the full 90 in all 12, out of the total 17 PL matches we played in this period. 6 goals he scored, he went 7 league matches without scoring, managing only 6 shots in total during that period...And we're acting like he was hard done by , christ, if Hitler got that many second chances we'd all be speaking German.
I'm not entirely sure how Lukaku can bring more to the table. He's a brute force striker. If he has the ball at his feet running towards goal at full pace he's extremely difficult to stop. He doesn't have the general technique to function well when there's limited space to operate in, the ball keeps bouncing off him or we end up with the extremely pathetic videos of Lukaku waiting for the ball to stop bouncing as if he was a 5 year old, he doesn't have the stamina and/or agility to function in a system where he has to press the opposition and his timing and use of his size when challenging for headers is absurdly bad.
Rashford isn't in any means perfect, but he has the basics to function in a system that the majority of fans want to see. A fluid attack with players that can press the opposition high up the pitch and swap positions freely. Doesn't matter if he's not as prolific as other strikers, if it's in a well functioning system we can still score plenty of goals spread over several players, instead of depending on one single player.
De Gea's form didn't collapse until the end of the season, we stuck by him because of who he is and the alternative on the bench.