Yeah, I get why they're opposites, but I feel other characters (BB, Sabo/Dragon, Koby) have a role to play in taking Imu down and there'll be a world post-Imu (as the Harley mural seems to imply Joyboy is the one in change of 'ending - see changing - the world).
Either BB and Luffy face eachother for the OP before the war vs. WG - which would only leave Luffy & co to face Imu and the WG - or they face them together (along many others) and THEN they fight to see who will '''''impose'''' their worlview on the world after Imu.