I would not look into the numbers at Chelsea, Lukaku in PL and Chelsea was not a match made in heaven.
Both Lukaku and Vlahovic scored 10 goals in Serie A last season, Lukaku in fewer games, he had a poor start with injuries but showed up in the last part of the season, looking like the Lukaku that scored 24 and 25 goals in Serie A during his first season.
You know Vlahovic scored 7 goals in 15 games his first half season? That's ok I guess. Last season 10 goals. Been bad for many reasons, we can blame injuries, Allegri yes. Still his fitness is a huge problem, a problem he had at WC and before, and even after, and sadly even now.