There's nothing really to make the fight significant. Luffy has shown no interest in Akainu other than a single panel 10 years ago and in the next panel he was over it smiling and eating meat again. He has never expressed any sort of desire for vengeance any more so than when he thought a celestial dragon killed Sabo.
He is also much too strong for Akainu at this point to make it an interesting fight. Luffy is yonko level now, Akainu is not. Simple as that. Luffy's major fights are about him overcoming challenges, not dog walking them.
Sabo on the other hand has shown huge amounts of cracks in his psyche when it comes to his brothers, he is fighting directly against the government and he is about admiral level. He also has his brother's devil fruit which directly links him to Akainu and overcoming his devil fruit advantage.
Sabo makes sense from both a power level and narrative perspective.