I actually think it was a huge mistake to let him go and it was even bigger mistake to do it without at least average replacement.
Many people will say that he didnt work in United, but is this even true?
Lukaku and his first season 2017/18 - he played 51 games, scored 27 goals and had 9 assists, overall played 4071 minutes, so he needed just 150 minutes per goal, 113 minutes per goal or assist. He scored 16 goals in PL (#1 in MUTD and #6 in PL).
Can you really say this was bad season or not good enough for main striker for ManUnited? It was hist first season in top4 club, first season under Mourinho and for me he did absolutly fine.
If you want to compare him with season before that, look at Ibra. In season 16/17 he was our best goalscorer with 28 goals (and 10 assists) in 46 games, overall played 3847 minutes, so he needed 137 minutes per goal and only 101 minutets for goal or assist. He scored 17 goals in PL (#1 in United and #7 in PL). And I dont remeber anyone saying he had bad season, that he wasnt good enough for us and that we need a better striker. Actually peeople were angry because of his injury that we lost one of our best players (and I agree). So was his really so much better than Lukaku who was according to many people nothing more than flop for United? Or the big difference is that Ibra came for free? Well, yes, it can be, he did cost us nothing, but if we want to rate players based on their transfer fees, we can start with Maguire or AWB and it wont look good, same goes to Martial or even Pogba and so on.
Btw year before Ibra (15/16) our top goalscorer was Martial with 17 goals and only 11 in PL, but that was of course LvG´s last season.
I definitely agree that he did not succeed last season, but who actually did? After all that negativity from Mourinho who was finger pointing left and right but himself, after all those broken negative records while all of us thought it could not be worse (Ole proved us all wrong but thats not the point)...Lukaku definitely failed that season, but he was just one of many, even de Gea had his worst season since his very first one and only good player was Pogba (manye people would not even agree with this one, so maybe shaw?). But if you look at his all time record, it was more like an exception rather than his usual standard.
Romelu Lukaku's record across all competitions:
2012/13: 38 games, 17 goals
2013/14: 33 games, 16 goals
2014/15: 48 games, 20 goals
2015/16: 46 games, 25 goals
2016/17: 39 games, 26 goals
2017/18: 51 games, 27 goals
2018/19: 45 games, 15 goals
And look at numbers from last season of our offensive trio:
Lukaku with 45 games, scored 15 goals and had 4 assists, played 3001 minutes, so he needed 200 minutes per gol, 157 minutes gol or assist (overall in PL he needs 170 minutes per goal)
Rashford with 49 games, 13 goals and 9 assists, played 3291 minutes, needed 253 minutes per goal, 149 minutes for goal or assist (overall he needs 209 minutes per goal in PL). This season is above his average as he needs only 134 minutes per goal, but that mainly because of many penalty kicks he scored, he scored 14 goals, 5 of them from penalty kicks and without tthose 5 goals, he would be on his long-term average of 209 minutes per goal.
Martial with 38 games, scored 12 goals and had 3 assists, played 2327 minutes, needed 193 minutes per gol, 155 minutes for goal or assist (and his overall stat is 212 minutes per goal in PL).
So I agree that Lukaku had a bad second season (as well as the whole team). He also knew that he would not be Solksjaer´s first choice and was forced to play as RW or as a CF in diamond, where a substantial part of his work was defending on the wing. But he certainly didnt have a much worse season than Martial or Rashford who stayed as our main striker for this season. So why he was reated as flop, donkey, deadwood and so on and those two got guilt free pass and became our first choices for our starting XI?
And is one bad season (or maybe only half of the season) enough to write off proven striker in PL? Does he really didnt fit in Oles system? And what kind of system he wants to play? Kick and run? Well I am sure Lukaku can do that too and actually could have bette dribble succes than James (who has worst in whole PL) and we would have one more option for our attack.
And I actaully don't care that he wanted out. Pogba also wanted out. I dont care about their feelings. They are our employees, we should do what is the best solution for us, not for them. We bought them for big money and we paid them fortunes to play for us, so if we need them, they ll just stay here and do their best. He had a long term contract, we didnt need to sell him and we didnt have a replacement for him. IT was horrible decision and it of course back fired, because while we suffer big time in attack, he is enjoying himself in Inter and already broke some record over there.
Ffs he already proved himself in WBA, Everton, Belgian international team, now in Inter and I would even say in first season with us. Looks like every manager out there is able to use him and is happy to have him except for just one and thats Olé...