Pretty sure he's arguing Blackbeard goes down. Next arc they fight the WG. Meaning Blackbeard isn't actually part of the endgame.
Why don't you actually try reading the entire conversation before butting in.
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First of all a general definition from my part: Raftel is part of the endgame, unless you think becoming PK is a side quest.
The final part of the final saga is all connected, we are not talking about Wano and EH, just to say one. All will be in the same timeframe and the same plot.
Now, BB and Luffy fight to become the PK, BB loses and then Luffy fights Imu? Possible, maybe even likely (surely would be easier to manage);
In some way both arrive at Raftel, both learn about the D. and the void century and then fight? Possible too;
Both do that and then fight the Gov.? Possible too, but since Luffy has to be the one to defeat BB (and Imu) and BB himself is a direct parallel of Xebec (and not Roger and Joy Boy), I don't think BB will get to fight Imu anyway.
In all of this, there is Buggy and the CG to consider too.
Regardless, for the reasons I said, what I am sure of is that Imu is the final villain and only PK Luffy will defeat him because of the words of WB, because what we saw in Oden's FB, because PK means freedom and Imu means oppression, etc.
Since BB, on the other hand, is not the man Roger is waiting for but is instead a Xebec 2.0, will fall in a GV 2.0.
Whether this happens before Raftel, in Raftel or after Raftel is all possible and honestly I don't have any idea because there are too many possibilities.