Dana White: B.J. Penn Underachieved ... Shoulda Been One of Best Fighters Ever

He's already a UFC Hall of Famer ... but B.J. Penn could have been EVEN BETTER ... so says Dana White, who tells us the guy had the talent be one of the greatest MMA fighters of all time.

We spotted White in NYC -- and asked if there was a fighter who had insane raw talent ... but didn't have the drive to reach their full potential.

"B.J. Penn," White said ... "B.J. Penn probably should have been one of the best ever ... to ever live ... to ever do it. B.J. was so talented."

"I think B.J. in his own words would go back and do things differently if he could."

B.J. was 28-10-2 in his MMA career -- but couldn't figure out a way to beat guys like Frankie Edgar (lost 3 times) and Georges St-Pierre (lost twice).