First, if you ask LeBron James, Cleveland-Golden State would have to become a rivalry at all.
LeBron, via Joe Vardon Cleveland.com:
“We don’t look at it as a rival,” James said. “They’re a great team. They’ve been the best team the last couple years, last three years.”
“It’s just the next game, it’s Golden State,” James said. “They’re a helluva team, like I said the best team in the league and they’ve been that way the last three years, four years, however long it’s been, I’m not quite sure. But, listen, you guys know, we don’t put all our eggs in one basket for one game.”
LeBron just doesn’t want the Cavs to become comfortable. They’ve beat Golden State in four straight games – the last three of the 2016 Finals and on Christmas – and could extend the streak to five today. Beating a rival that frequently is a cause for celebration, and celebration leads to contentment. LeBron would rather keep Cleveland focused and hungry. Hence, saying the Warriors aren’t a rival.