It doesn't contrast shit. Arguing means fuck all. Jabra and lucci were the ones who argued and lucci slaps jabra.
Lucci, Kaku and Jabra are a perfect example.
In that case, Jabra's attempt to compete with Lucci was immediately cut off, and he was switflty relegated to a competition with Kaku.
That's like from their very first interaction, that Oda does the switch and from that point Kaku and Jabra continue to interact with eachother in that manner.
Exactly the opposite happens with King and Queen. In their case the third character Jack being used to contrast with both of them as someone who is that much weaker and unable to stand up to either of them.
So Kaku is brought in EL to difuse any hope of rivalry between Lucci and Jabra by showing that even Kaku is a bit stronger than Jabra, while Jack is brought in Onigashima to highlight how much stronger King and Queen are than him.