The way you're describing it, Akainu will be a final villain as in he will be one of the last people Luffy fights, which, about as relevant as Blueno being one of the last people Luffy fought before TS. Dude came after Crocodile and Enel, but still a fodder to them.
Absolutely yes and i believe he will. If Akainu and Imu fall in the same arc then Akainu will be the last 1v1 Luffy will have before advancing past and challenging Imu. The dynamic of a final war of a series can't be compared to that of previous arcs.
you want Akainu to get any hype from being one of Luffy's opponents, he needs to be a major antagonist, which is only possible if he's the main boss of his own arc.
As i said. I believe the Navy will be taken down at the same final battle but at different times and places, that's the key here. The battle vs the Navy will be its own battle, Imu or the Gorosei will be not included as they will deal with Dragon and co at the meantime. Akainu does not need his own arc, there's no time for that.
Oda used two Yonko to force Zoro to use the Mink medicine or whatever. You're reading manga the wrong way if you think Luffy will need that kind of shit against Akainu after defeating Kaido, Kizaru, and Blackbeard. I am all for Akainu wank, but he's not that guy.
Missing the point. Oda created a magical BS plot device to get Zoro back at 100% because he had to face a battle shortly after that. An asspull was required and that same might happen to Luffy.
Oh and i totally disagree. Akainu clearly is that guy to fulfill all of my expectations.