You don't have a single bit of evidence that Im is even a fighter.
Everything else doesn't make sense at this point. Luffy is already reaching a level of being potentially the strongest. And Im seems to be the counterpart to Joyboy.
Yes Luffy needs to fight the man who broke his will, scarred him physically and mentally and who has been paralleled with Blackbeard throughout the whole story.
Chapter 650 is your worst nightmare.
Actually, 650 isn't that important. In fact, the first time Jinbe mentioned Akainu's and said he had a fight with Aokiji, Luffy wasn't triggered at all, rather curious:
His scar only itched as he heard of Akainu emerging victorious. But scar-itching is a common theme; Kaido's scar itched when being reminded of the long dead Oden, Shanks' scar itched when he watched Blackbeard.
Also, what was the narrative during and post the war and post timeskip?
> Luffy overcoming his trauma, remembering his friends, wanting to become stronger
> Shanks saying to Luffy that it is ok to cry, but after that a man should move on
> Ace living and dying without regret, accepting his fate as a pirate
> Luffy relying on others, as "making those around him his allies" is his biggest strength
> Sabo inheriting both Ace' power and will, with people commenting on how similar Sabo and Ace are,
> With Sabo regretting he could not save Ace, and although forgiving himself, upon roasting Burgess, saying that it seems that Ace however still hold grudge.
So I don't see how Luffy, who now became Joyboy, will beat Kaido and be basically lead the world against the WG, will be the one to face Akainu due to some past conflicts.