Execpt this isn't true. He wasn't the best player the 1st 3 months of last season, he was scoring goals at normal ratio given that he was the central striker and was playing every munite of every game and some people were falling in the trap of thinking he was amazing. Someone like Martial was putting better performances and had bettre stats than him despite coming from the bench, he then went in a long spell of 2 or 3 months without scoring and looked horrible but this was overlooked becauce we were busy spending our time comparing him with another average striker in Morata. At his best, his level still below of the like of Aguero, Kane, Icardi, Suarez, Benzema, Cavani, Mbappe, Lewandowaki, Aubamyang, Lacazette, Grirzman, Costa, Mandzukic, Firminho, Mertens. Actually all other big clubs have better strikers than him. Working hard isn't a barometer of good performance, Messi is actually one of the lasiest player in the planet but still head and shoulder above everyone.
Nobody denies that he's able to score goals, but it's his overall game that's in question. Scoring goals alone isn't good enough for certains style, Zlatan was scoring but it didn't stop Pep from kicking him out. Lukaku inability to control a ball and his lack of stamina make him a liability.