@fullscalenuclearwar:
X-drake from Supernovas was a Marine Rear Admiral.
There's a huge difference between the two.
Hell there's a big difference between an admiral and a vice admiral too
Also what makes you think that Aokiji has to have a dream of travelling to the end of world? Robin, for instance, want to find out the history of the void century not really sailing to the end of everything. Aokiji could just figure out some secrets Marines are trying to hide thus travel with Strawhats to find the true history? If you think this is not plausible then fine.
It's pretty obvious that raftel has a lot to do with the void history, and Robin knows this too. Think back the Gold Roger's message on the bell-fry, and Rayliegh's words to her.
And we don't really know what Ao-kiji's motives at this point. He left the marines only because he didn't want to serve under Sakazuki. Implying he might have had some sort of tacit consent about the WG's past. OR he was just completely ignorant (which seems unlikely). Maybe he will try and uncover the past, but that's pretty weak speculation (at this point) and doesn't serve as a good basis for a potential crew-member at all. Not that it makes any sense that an admiral would join a bunch of NW rookies to do so in the first place.
Keep in mind that we haven't seen anything to suggest that anyone other than Robin, like Ao-kiji!- knows about the potential secrets that raftel has. If he were so diametrically opposed to the marines he would join the revolutionary army.
Btw I doubt it's appropriate to say Luffy is still few levels below Aokiji, I mean, after 2 years of learning Haki & given he can hit a Logia now(Caribou), I'm not saying he can really defeat Aokiji but he could at least pull a good fight.
Strong as he is Luffy would still lose badly against Ao-kiji. This dude permanently changed the weather of half an island. Having someone that strong with them would mess up the whole crew dynamic and would mean smooth sailing until they hit people like the Yonkou or Aikanu. Why do I even have to say this.