KD already a much better free throw shooter.
He's a much better shooter, period. The only other person with that kind of size and shooting ability in the game at the moment is Dirk.
If you're talking about range, then Rashard Lewis, Steve Novak and some more are 6'10"+ and great three-point shooters (and probably FT shooters). Of course, if you talk about mid-range game, then those guys I mentioned don't have it.
But Dirk is even taller than Durant (7'0" vs 6'10") so if you're correlating size and shooting ability Dirk is more accomplished (he is the tallest elite-shooter ever?).
I'm talking about guys who can hit tough shots from anywhere on the floor even when they're the main focus of the offense and the opposing defense. Guys who can regularly score 20+ points a game primarily on jumpshots. Guys with fluid form that hit the kind of shots that make you think "dang, he's unguardable."
Fair enough. Then you're definitely right (but there could still be a 6-10er that could hit these kinds of shots - don't think anyone as tall as Dirk will ever be that good though).
In response to the main topic: Durant's ceiling, in terms of scoring, is probably higher than Lebron's (especially if he adds bulk and a few more post moves) - of course, Lebron could get better offensively quite quickly as well if he gets some post moves, improves his jumper and his FT%. But I give that one to Durant.
Durant could definitely be as good a defender as Lebron. His relative lack of athleticism (to Lebron, not to average NBA) is made up by his length. A tie (assuming Durant does reach his potential - Durant is below-average after three seasons, while Lebron was at least mediocre as a rookie, and has kept improving since).
Rebounding , Durant may have the edge. We have to remember, this was just one game (the 19-rebound one), his previous high is 15. His average is 7.3 (LBJ averaged 7.6 in his third season), playing with a poorly-rebounding frontcourt (Krstic and Green). But he does have long enough arms to be great at this.
But the main thing that separates LBJ from Durant is his passing/court vision and unselfishness. Kobe will be surpassed by LBJ, but this may not have happened if Kobe was unselfish - he had great enough court-vision to be a wonderful teammate, but he decided to ball-hog. Durant is not selfish, but he is a poor passer. This is probably the hardest skill to develop, and it's unlikely Durant will ever attain even 3/4 of Lebron's level.
KD will be second-best in the league soon. And very close to Lebron. But Lebron is just special.