There is no denying that the Lukaku we see now at Chelsea is a fitter, leaner and improved version of the one we sold. Given that United Lukaku even at his worst had almost 20 goals to his name, he will definitely make a difference for a far better Chelsea side.
However, his basic weaknesses of poor first touch, big game droughts and fragile mentality still remain. Unless he improves on them, he will always remain a tier below the top center forwards. And he will blame everyone and everything to avoid accepting that, just like he did with us here.