It is true. LeBron James is the best basketball player ever. Here is how I came to the conclusion:
First looking at them in their respective eras:
-Let's use PER as a starting point. They each have a single-season best of 31.7. Jordan's career average was 27.9; LeBron's: 27.6. But LeBron came straight out of high school, so I'm going to say this is a wash
-The main element that PER neglects in individual defense. LeBron has the edge here. Don't forget about his unique versatility. He's bigger than Jordan but just as fast. He can shut down Derrick Rose, Chris Paul, Pau Gasol, and Al Jefferson. In guarding wings, LeBron and Andre Iguodala rank 1-2 over the past few years in advanced stats. (This doesn't even account for his versatility.)
So, I think LeBron is at least as good in his era and, once you compare eras, it's no contest.
-Magic/Bird/Jordan made the game a lot more popular. This led to a higher degree of competition a generation later. Kids are playing basketball way more today than ever before. NBA players are bigger, stronger, faster, better-practiced Technology is better. Players get far better medical treatment.
-The pace is much faster, skewing the per-game numbers (that's why PER is good). The fastest teams today (Nuggets, Rockets) would be the slowest if they played in the Jordan era. Increased pace is unfavorable for superstars/domination. Everyone is more tired, has to rest more and more players get involved.
-Players actually play defense now. The evolution of NBA defenses over the last decade has been remarkable. There is FAR more motion involved in playing defense. Defenses have gotten smarter and received more attention/effort. This trend has been led by Tom Thibodeau, who started sending an extra defender from the weak side, a very effective move, which, nonetheless, requires a ton more motion for the players to rotate.
So, basically, LeBron was at least as good as Jordan, in their respective eras. And if you take, era into account, it's not even close.