Kaneshiro's words plus the ending where Joker takes Yaldy's offer just further emphasizes that Joker could have very easily turned out to be another Goro if not for the rest of the PT
Because Ryuji and the other PT all agree that they're nothing like Kaneshiro; that they would never take advantage of palaces for their own sake, but that's what Joker does in the ending where he takes Yaldy's offer
Joker: Oh, nice