Nah. It is its own form of fallacious reasoning to scream "correlation is not causation" when the evidence of causation is starring you in the face. Lukaku's absence and our failure to replace him is the biggest factor by far (though, obviously, there are others).
Of course but there is a massive hole in our team because we didn't replace him. Think it's more about how inept that decision was than how good lukaku is