The Belgium international joined United in July 2017 for an initial £75 million, but he moved on to link up with Antonio Conte's side this past summer and has enjoyed a return to his scoring best.
Lukaku, 26, told reporters at the Global Soccer Gala in Dubai, United Arab Emirates: "The period there had made me calmer. I don't look at it in a negative way; it really helped me mentally to be ready and to grow as a player and as a person. I will never see it as a bad experience because it helped me be where I am today."
Lazio frontman Ciro Immobile leads the Serie A goal charts with 17 goals this season and is the only player to have scored more than Lukaku (12 goals) thus far in his maiden Italian campaign.
Inter are level on points with Serie A leaders Juventus and only trail via head-to-head record. Lukaku illustrated his importance to Conte's plans just before the Christmas break, when he scored his 200th career club goal in a 4-0 victory over Genoa.
The forward continued to discuss his development as a result of the challenges he faced at United, for whom he scored 42 goals in 96 appearances (0.44 goals per game):
"Clearly now that I'm at Inter there are benefits from what I learned in Manchester both from a sporting and non-sporting point of view.
"I prepared a lot and I am much calmer. In my head, there is much more serenity and composure.
"I am a person who when things are not going well, shows it through so much anger. I'm stronger after the Manchester United experience."
The Red Devils parted ways with Lukaku as they looked to move in a different direction with their attack, and it now appears as though the separation has yielded positives for all parties involved.
Ole Gunnar Solskjaer's side have adopted a quicker forward line consisting of Marcus Rashford, Anthony Martial and Daniel James, who have looked like a more menacing threat in the Premier League.
Lukaku scored a career-high 27 goals during his maiden campaign at Old Trafford, but scrutiny over his performances grew after he bagged just 15 times in 45 appearances last season:
He's almost matched that figure this term having scored 14 goals in only 22 appearances for the Nerazzurri, regaining the kind of swagger that previously made him such a hit at Goodison Park.
Lukaku scored two and assisted another in the recent hammering of Genoa, where his second strike demonstrated the return of his confidence, via Premier Sports (UK viewers only):
His time in Italy hasn't been without incident, however, and Lukaku also told reporters at the Global Soccer Gala he would like to see cameras used in Serie A to identify racist abuse, having been subjected to such behaviour already. The Belgium international had monkey chants aimed at him from sections of the Cagliari fanbase in September during a 2-1 away victory for Inter.
Lukaku's current scoring pace suggests he's on track to break his own single-season scoring record in his first term with Inter, using his struggles with United as an aid to fire his way back to the top.