Like the OP I also feel pretty strongly about this. I've heard that the NBA testing program is a joke. The league has zero interest in busting anyone for this, because if PED use really is rampant in basketball, they certainly don't want that to become a story. And like the NFL, if PEDs are making guys more explosive, then the entertainment value will suffer if they clean up the game. Recall how hesitant the MLB was to deal with this problem. No one cared when Sosa and Maguire were chasing Roger Maris for the homerun record. The MLB only got serious about testing and punishing when the US Congress got involved.
I think PED use is rampant in basketball. Might have been back in the 90s, for that matter, but there's no question in my mind it's more prevalent now. To do as much aerobic activity as these guys do in the course of the season and end with as much muscle mass as some of these guys have... I just can't believe it's all natural.
On Lebron in particular, at this point I'd be shocked to hear he's not on something, and loads of it. There are so many bits of evidence on this, including the shape of his face. But the kicker for me is the athleticism that he showed late in the postseason, when everyone else was gassed and/or worn down, at the age of 31. That alley oop he caught seemingly above the top of the backboard, I think in game 6. And more subtly, that attempted dunk on Draymond Green in the last minute of game 7 where he was fouled; I think he was about 13 feet in the air. The dude is basically the equivalent of the racing car that's curiously faster than all the other cars on the track. Bigger, stronger, and faster than all other world-class athletes. It's so common to just say "Lebron James is a physical freak!" But given the doping scandals we've seen in sports in recent years, I think it's extremely unlikely that the guy who's head and shoulders ahead of every other world-class athlete in terms of physical ability is clean. Sorry.