As I remember, It was the 2012 NBA finals where they poorly executed from coaching staff down to the players. I dont know what actually happened during that time but Lebron was averaging his lowest in the playoffs I guess.
It was 2011 Finals (Mavs def. Heat).
Wade was still taking the lead but when he was hurt, Lebron could not fill in his shoes at the time. Their newly formed team was exposed by the Mavs whose core team remain largely intact and they have been firing on all cylinders. I also remember what the Mavs coach saying the two teams have different playing style, the Heat playing in the air and the Mavs playing on the ground. The game wan won on the ground.
That was the only championship of Dirk and I love that series though I lose my bet since I bet with the Heat to win in the series.
I can't remember who's the favorites that time as I made my bet offline, with my friends to be specific.
After that, we've seen how the heat has improve and if I not mistaken, they were the champion in the next season and that was because Lebron, Wade, and Bosh make this team a better one, also credit to the role players of the Heat like Udonis Haslem who were so good that time.