And you still don't get the point. Akainu and Blackbeard have different roles. BB is Luffy's main pirate fight for the Throne while Akainu is Luffy's main Marine fight. People can run from it as much as they want, the scar is there for eveyone to see and it connects them.
Akainu fighting Luffy does not invalidate Imu's role. Lol at the Gorosei, those fuckers will be beaten by the other crew members i reckon.
Don't care about your admiral boner
Imu - potential final boss trope with the highest order of the world bowing to him, casually wiping out an island (whether he has Uranus or uses it, the details remains to be seen but already far more important than Akainu)
Blackbeard - D Clan, a threat to Imu, the only known character who hase broken the df rule, literally Luffy but if he was Evil.
Gorosei - bowing to Imu, might act as his potential personal guards, Highest class od World Nobles, Calamity equiavelnts to Imu if he becomes final boss.
All three groups with ties to the void century
Akainu has nothing unique to him for a final boss trope. The only thing he has is Luffy's scars, but Sabo is for that, not enough to close the series in a finale compared to the other groups above mentioned.