It's a huge statement coming from Johnson -- after all, the Golden State Warriors won 2 'ships with the offensive juggernaut of KD, Steph Curry and Klay Thompson ... and very well could have won more if everyone had stayed healthy.

JJ says the entire league -- including LeBron James' Lakers -- will struggle to stop Brooklyn's trio of superstars ... but there's one major issue keeping them from being a lock to win the Larry O'Brien trophy this season.

"They can score the ball, it's just getting stops," Johnson told us at LAX on Thursday. "That's gonna be their biggest problem the whole season."

Johnson isn't ready to call them the best overall big 3 in the game, but scoring-wise?? Hell yeah.

"No question. The best three isolation, get-a-bucket -- yeah you're not gon' get better than this."

When asked what this means for LeBron's quest for ring #5, Joe keeps it real.

"S***, they're gonna be a problem for any damn body. Not just the Lakers. But, like I said, the Nets, they'll figure it out over the course of the season and they'll get things rolling. Right now, they still tryna find themselves."