UFC star Israel Adesanya is a phony champ who hasn't beaten any level fighters ... so says Paulo Costa, the dude who just beat Yoel Romero.
TMZ Sports talked to Costa -- the #2 ranked UFC middleweight -- about his next move after his epic win over Romero ... and it's clear he ain't impressed with the 2 champs in his division.
"Yoel Romero is more tough than Whittaker, I know. And, man, Adesanya, Adesanya is a fake champion."
Why does Costa -- the 28-year-old undefeated (13-0) fighter -- think Izzy's a fake champ?