Akainu vs act 1 Luffy -> One Piece is already over because while Luffy was knocked out after that Bagua, he wouldn't have a head in this scenario, had Akainu been the one to connect the hit.
Akainu vs scabbards ->They get destroyed and they all either die or are pretty much put in a death bed with a hole in their body. I doubt they will even connect a hit on him. The scabbards were lucky that Kaido stayed in his dragon form so long.
Akainu and Big Mom against the novas-> Once again, these 5 are screwed. And the thing with Akainu is that, again, even casual magma punches are potentially lethal.
Akainu vs Luffy on the rooftop -> Luffy obviously loses. One of the differences with Kaido is that in this scenario Luffy would fall in the sea without a head, just like in the first scenario.
Akainu's powers are simply terrifying to deal with, both in a 1 vs 1 scenario or in a group scenario. It's not about Akainu vs Kaido as a whole, even though I think Akainu is stronger regardless.