Sabo has no conqueror's haki, and nothing so far into the story suggests he has.
And he has a DF disadvantage against Akainu.
As far as we know, Sabo is just a logia user with advanced armament haki, maybe future sight. No different from guys like Aokiji or Kizaru in this regard (I won't rule out conqueror's haki for Akainu just yet)
Considering these, Sabo beating Akainu solo would be the biggest disrespect that Oda can give to Akainu.
It would be fine is he just played a role or land the final blow tho, just not a 1v1
Ace, Sabo, Luffy are the brothers trio. Both Ace and Luffy are conquerors; as a kid, Sabo and Ace were near equals.
Sabo then received Haki training from Dragon whilst Ace received a logia. Then Sabo received the same logia. Sabo's potential was high
before he inherited Ace's will - now it's even higher.
Furthermore, the only parallel to the brothers trio are Roger, Whitebeard and Oden - all three are ACoC users.
Sabo has high top-tier potential. We know this because Luffy is a mid top-tier and Oda still wants Sabo to be viewed as Luffy's superior in the eyes of the world. Luffy just defeated the WSC and Oda gave Sabo the better hype, such that Luffy remains Sabo's little brother. Whether the hype is real or not, it's clear that Oda has plans for Sabo - he's already surpassed Dragon in notoriety, it's only a matter of time before he surpasses him in strength too.
Sabo vs Akainu with a matchup disadvantage is quite honestly the only EoS fight that would make sense for Sabo as he has PK potential - especially now that he's inherited Ace's will - and everyone else would be too weak for him.