James was in a different situation....Durant had a stacked team in OKC...Durant was 1 game away from making the finals before he choked....
Lebron had to leave, when he left the cavs they were getting older, and had been going backwards in the playoffs losing in an even lesser round from the year before....and lebron carried the heat in every statistical category....durant is just tagging along
No one is saying Lebron didn't have to leave to win titles. It was pretty clear when he left Cleveland that he wasn't going to win any titles staying there. His choices at that point were basically...leave, join a stacked team in Miami and have a great chance at winning titles...or stay in Cleveland and end up being like John Stockton or Karl Malone.
No one is even saying that he didn't have to leave the Heat to continue winning titles. It certainly looked like the run was probably over there as well (especially with what's going on with Bosh's health). Had he stayed, it's likely they would have made the finals because of how weak the East is. But the days of actually winning a title in Miami were likely over unless Riley had a minor miracle up his sleeve.
No one is even saying that he was wrong or is criticizing him for leaving. In both cases, he fulfilled his contracts both in the number of years he played and in how hard he played and tried to win for those teams.
What is being said is that he joined stacked teams and Cavs fans are being hypocritical when they criticize KD for doing the same thing.