The Los Angeles Lakers were busy this offseason ... but Kenny "The Jet" Smith doesn't think their new additions will fill the gap LeBron James is leaving behind, 'cause he tells TMZ Sports their new roster doesn't have enough to compete for a championship.

We caught up with the NBA champ and "Inside the NBA" analyst out at LAX this week ... and asked his thoughts on the state of the Purple and Gold.

The Lakers brought in Walker Kessler, Collin Sexton, Sandro Mamukelashvili, Quentin Grimes and re-signed Austin Reaves so far ... and Smith said Luka Dončić and the crew will definitely be a playoff team -- but that's about it.

"This is a competitive team, but not a championship team yet," Smith said. "LeBron James makes them a championship team."

We threw out the idea of James somehow getting back on the Lakers -- even though both sides said their goodbyes last week -- and Smith said with this group of guys, they'd be legit contenders.

As for the "Snowtime Lakers" nickname going around online ... Smith has some words about that, too.