Shouldn't Rengar of been a Battlecast skin to rival Mecha Khazix, not a part of the same skinline?
Lorewise, I'm fairly sure it was stated that the PROJECT/Mecha/Program/Battlecast skins were made in the same universe. Humans have been augmented for the PROJECT skinline, Yordles are responsible for the Mecha skin line to defend their home, Battlecast is Viktor's uprising of the "Glorious Evolution" and Program's are AI's under Lissandra's control of a hivemind queen.
If this is the case, wouldn't it of been more thematic to place Rengar in the Battlecast line? It's kinda confusing having two rival characters being a part of the same skinline, I don't think they'd play along well.
Potentially retconning Khazix to the Battlecast line would fit his thematic as well, since he's inherently all about evolution and would solve the issue. I'd doubt that'd happen however.