I don't think there's much rewriting going on. The people who were shitting on Lukaku when he was here are the same people who are still shitting on him now that he's banging them in for Inter, or at least they're keeping quiet.
I thought he did fine at United, at least compared with his teammates (which is the only fair comparison, seeing as we're such a dysfunctional team. I'm pretty sure most players would do better at other clubs), and the fact that he's scoring goals for Inter is the least surprising thing in the world. It's not like that's an easy task, either, their lack of goals is what has separated them from the best teams. Going by Wikipedia Icardi was their top scorer last year with 17 goals, the only player to reach double digits. That's in all competitions, not in the league. In the league Icardi scored 11, Lukaku has 9 after 11 rounds and only trailing Immobile.
I guess that's why they bought him.