Melo definitely didn't have it coming in. He was played at the 4 in college and played down low in the 2-3. He was a terrible defender coming into the league. And Lebron wasn't much better, he hadn't played much defense before coming in to the NBA.
I agree that they both had bodies that fit their positions but Durant does too outside him just being too skinny right now. Like I said, with strength work he will improve his strength and his lateral movement enough to be at the very least an adequate defender.
Your first paragraph insinuated I said they were both good defenders. That is NOT what said or even implied.
Your second paragraph is EXACTLY my point. We just disagree that he can develop his body. Even Prince was "thicker" (and quicker) coming in than is KD. I've known A LOT of guys with his build, although they didn't have the financial resources of KD, and they just never could change what they are/were...
We'll know the answer in about 2 years.