Perhaps Tuchel and Conte know more than we do?
Perhaps Tuchel and Conte know how to use Lukaku and how to get wins with him in the team, while Ole doesn't?
When you are trying to assemble the best possible team, you need some specific ingredients, depending on your specific plan. You don't really need the best of the best in every single position, this is usually not feasible, and sometimes it is really not the best for the team. You need the right ingredients, and you need to know how to use every player to the benefit of the team. Obviously, the most important role is to get goals, easy goals, tap-ins whatever, but get some goals especially against mediocre teams. That's how you don't lose to Aston Villa at home, you have someone like Lukaku who scores a couple.