Read through some of the last pages of comments - and I want to chime in.
A player like Lautaro is what I call a 'complete' striker. By that I'm not referring to their overall level of skill, but at the range of skills they possess and the amount of different tasks they can be ordered with. Lautaro can act like a target man, he can act as the advanced forward, he can make runs, he can connect, he can do it all. But he doesn't excell at anything individually - which is also a reason why if he has a bad game, he disappears for 90 minutes. Lukaku, on the other hand, is very much defined in what he excels at, and what he is poor at. We don't have to go indepth, but we know Lukaku has high pace, insane strength, high jumping reach and is good at finishing and heading. Importantly to add, he also has the right personality for our team, something which is usually overlooked. We also know his weak points: first touch, dribbling, passing to an extent and composure. Yes, I do not think the problem lies in his ability to finish, I think he's a pretty remarkable finisher, but he lacks composure. He's not a finisher like Icardi due to that, but he possesses different qualities.
I think the problem with the discussion on Lukaku's weak points, is how people view football. Not the way in which they view it, is the problem, but it's the direct causation. If you would poll to the crowd what type of football they prefer, tiki-taka or hoofing route one, we all know the outcome. Technical skill is the most (over)appreciated aspect of this game and it's what makes football very enjoyable to watch. Lukaku is limited in some of his technical aspects. We can criticize him, but we have to tell ourselves if there's any merit to it. Lukaku will never be a tiki-taka player, no matter how much better he gets at his technical abilities. He will likely never get his composure to the levels of Icardi, and he'll never come deep to get the ball and dribble like Sánchez.
But there's simply more to football than that. Good luck asking Icardi or Sánchez to use their body weight to fend of opponents or knocking the ball past their opponent at high speed. In fact, in some aspect Lukaku is a unique player. One of a kind. How many players are AND tall AND have high speed AND are strong? Usually this is a question of two out of three. I don't think there is any player currently like this - to that extent of excelling ability in those factors.
I think, despite how much critism he deserves, Conte is the biggest contributor to the Lukaku we know and see today. He is the first one to play him to his absolute strengths, and it shows in what kind of numbers he puts out. We've seen stats posted here of Lukaku's goals/game and seen questions raised around them. No one has ever gone into full analysis, and I think it's good no-one did. Because the outcome would likely be that we cannot deduct a thing. The only thing to keep in mind on the debate whether 'how useful' his goals are, is to judge the team as a team. And not the team as Lukaku. There's always 11 players on the field. If Lukaku scores 2, we concede 3 and lose, next game Lukaku isn't on the field and we win 2-1 - you cannot conclude that we have a similar output without him on the field and he's not helping his tip over the edge. Lukaku is not our primary defender and it'd be highly surprising if he's to blame for any of the 3 goals against. This requires a much deeper analysis than what anyone has tried to cover here. Moreover, Lukaku was also joint 3rd last season in Serie A in terms of key passes (
https://imgur.com/a/AZ3AiQY), you know something we'd love to see out of Eriksen.
The question also rises in how much Lukaku is to blame for his 'underperformances' against big teams. The answer is roughly the same. There's 11 players on the pitch. And we know Lukaku's poor technicals will not help against better teams with better defenders. However, his outputs in these games are also directly linked to the team contributions. If Lukaku cannot get himself into the perfect place alone, his team mates should help him right? But they will also struggle more against better teams. People tend to think of Lukaku as a great striker, but not world class. But the question is, does that matter? Lukaku can win you a Champions League, just as likely as he can fail you to win a Scudetto. Why? Simple, because of the players around him. If you use Lukaku as your primary carry and only player, then yes. Expect no major trophies. He is not a perfect player and part of his skillset does not suit every trainer. But if you have a great team around him, he's a striker who is capable of going the extra mile. There are worse strikers who've won major trophies than Lukaku. Team (play) is more important than the player.
With how de Vrij, Handanovic, Lautaro, Kolarov, Perisic, to an extend Hakimi and probably others have been underperforming this season, I see no merit in looking at how Lukaku's incompetencies are potentially holding us back. I think there are currently bigger problems at hand.