After the alliance beats Kaido and probably Big Mom (if there is no detour to Elbaf), and after seeing what those monsters could do, does what Green Bull would do matter at all? I mean we are not in the stage to be awed by Admiral entrances anymore isn't it?
I don't know, we witnessed what Whitebeard pulled during the war and the consensus during Dressrosa was still that Fujitora is bonkers. But being awed by the last Admiral's powers is not what I consider the inevitable event at this point, that's up to each reader anyway. What I think is unavoidable is the usual show of force that establishes why he's among the most powerful individuals in the world, and each Admiral had at least one chapter dedicated to him alone to prove it.
And these massive displays of power escalated over the years, appropriately to the growth of the crew:
Aokiji effortlessly overpowered the Straw Hats while freezing the sea for miles around him (at that point Luffy already beat two broken Logia fruits)
Kizaru destroyed a large part of Saobody the moment he arrived (by "mistake") and then proceeded to effortlessly beat a group of Supernova, at least half of them strong enough to get Warlord invitations. The Admiral arriving ended with the ultimate defeat of the Straw Hats, they were only saved by Kuma hax. (at that point in time Luffy defeated yet another Warlord and a CP9 agent considered to be in the same ballpark)
Akainu had his grand entrance in the war, with characters involved who were stronger than him. He had his extraordinary moments simply by getting shit done, in a war scenario with countless skirmishes and unfinished clashes. His show of force as an Admiral was not only based on his powers, but attitude. He defeated Luffy AND took something away from him that can never be fixed.
Fujitora had an entire arc dedicated to him, everything that happened in Dressrosa happened on his mercy (which hurt Doflamingo as a villain in my opinion, but it is what it is). And after dozens of chapters with some meteor summoning and gravity crushing, he destroys an armada by throwing every piece of rubble on Dressrosa on them. He cleaned house.
So what do we expect from Greenbull after this? "Hey I'm the new Admiral, I haven't eaten in 3 years because I can turn into a fern. Believe me I'm very strong :happy:"?
I mean with the 5 year clock ticking the options are few. Oda could save his introduction/show of force for the mega-war, but he wouldn't be able to distinguish himself like Akainu did, who "awed" the reader by actually killing important characters - in One Piece!
I can't picture Green Bull doing that, at least not in a Ace-style manner. He's just not important enough to be the focus of the endwar, unlike Akainu during the Whitebeard war.
So what is left if the endwar is too convoluted for a focused Admiral introduction + Greenbull not being important enough as a character (outside of his role as a living weapon)?
An Admiral introduction Kizaru / Fujitora style. He arrives at Onigashima and cleans house. At that point Kaido & Big Mom will be defeated already (not killed), but someone needs to remove them from the grand stage. Who's supposed to do that? Drake…?
- whatever forces are left of the New Rocks Alliance. There are thousands of pirates currently present after all.
So I imagine Green Bull flexing his powers like Fujitora, with the new Vegapunk weapon being his version of Kizaru's supporting Pacifista squad.