Rivalry? LeBron is a steroid user and a fraud. He came up during an era when guys like Barry Bonds were abusing historical records without consequence. He has been allowed to cheat - both with his body mass and with his infamous off-arm during drives - more than any athlete I've ever seen.
Now he is funneling cash into the league and its sponsors via a city that never really wanted him.
David Stern created LeBron, and Silver is using that puppet as a cheap comic book villain.
What the Steroid King and his "Space Jam 2" partner Anthony Davis do is inherently meaningless. Especially to a classy organization like the C's.
So no, there is no rivalry. When the C's start getting fraudulent #4 draft picks in a critical trade market and are allowed to cheat at will, maybe. But for now, the Celtics and Lakers are in completely different classes. The Celtics are a basketball team. The Lakers are entertainment.