I do remember him having a field day against Lukaku earlier this season as well. He is more suited to play against these static, immobile attackers.
Static players who can't jump. But yeah, Chiellini being back should light a fire under his ass because once Demiral got injured he settled into mediocrity, he's one of those players who needs motivation to keep his concentration.
I criticise him a lot because he's supposed to be a leader, yet he is not like Chiellini who always plays in 6th gear. Hell, even De Ligt is almost always on his toes and awake. Bonucci can switch off and coast, and when he does that he can become a liability in the wrong game.
At this point in his career he's not ever going to be some aerially dominant defender, he's not athletic or aggressive like that, but if you are not going to win a header you have to make it as difficult for the opponent as possible to either score or direct a flick on - a nudge or anything to unsettle them, not just jump and close your eyes. You CAN'T play as a central defender at an elite level and half-arse it on deliveries into the box. It's telling that he is markedly better at attacking headers - that's because he wants to win them and get a goal or goal chance, he's naturally an attack-minded player. Wanting to defend takes a special breed of nutcase. Obviously he was great in a back three because he had proper defenders either side and he could play as a sweeper and covering defender, but he's gradually got more used to playing in this back four over the last few years.