If by most prolific you mean almost 2 points per game less than Lebron at the age of 20, then you would be correct. BTW, Lebron also grabbed almost a full board more per game and dished out over 4 assists more per game. And Lebron's team won almost twice as many games.
1) I said arguably... meaning in the same group as LeBron, not better
2) LeBron was 21 most of his second year. Despite coming straight from high school, he was actually older than Durant when he entered the league.
3) Durant actually scored more points per 40 minutes than LeBron.
4) Rebounds were basically the same.. 6.9 to 6.7 per 40 minutes.
5) Durant was a more efficient scorer and significantly better from 3PT and FT
6) LeBron was a much better passer, yes
7) LeBron's Cavs were still a lottery team, but he had better players around him. Durant's team was in such bad shape they had to move to OKC!
Obviously Durant has a huge task ahead of him to match LeBron's career, but his 2nd year is right up there and his 3rd (at age 21) hasn't happened yet.