Lukaku has stated he bulked up on purpose for the World Cup. This was fine for the slower paced International game but an absolute disaster in the Premier League.
In relation to Serie A I think he'll bang in goals there as the league is slower and weaker but it means nothing to me. He behaved terribly to engineer his move and didn't seem interested in slimming down (cos he was still massive when he came back for pre-season this year) and didn't suit Ole's style of play.
Its a shame what's happened to Sanchez's form and I think he'll be lucky to get into double figures, even in Italy, but good luck to him.