We got 6ix9ine Sunday at LAX -- without incident this time -- where he was telling our camera guy why he was the biggest success story in rap, claiming he's won every battle he's been in (literally and metaphorically, we're guessing) ... and that he's never taken an L.

Big wigs at Barclays Center and TUNES Audio might claim otherwise for one reason or another -- but Tekashi's got the ultimate proof (allegedly) ... he says he's on 'Ye's forthcoming studio album, which is set to drop later this month.

You'll recall ... Tekashi said he was on his way to see 'Ye late last week, and if that was true ... it's possible he laid down a track with him right then and there. Kanye did exactly that with T.I. not too long ago during a visit, so it's certainly not out of the question.