As things stand Sanji not defeating Page One is a very real possibility to me, which I wouldn't have said before
This is not a case of the anime extending a fight, but it still having the same outcome. The manga never showed the conclusion of Sanji vs Page One, and nobody in the manga has ever said that Sanji did defeat them. We had assumptions of what happened in the fight, but no actual proof. If anything, everyone seemed to think "maybe the anime will show how Sanji beat him since Oda hasn't." I think if they'd done that, nobody would really have commented on it.
But now we're in the position where the only conclusion to the fight we have is the anime one. And in that, Page One was very much undefeated at the end of the fight. So the question is, did Oda tell them to do that? Did he say "by the way, Page One is going to have a fight at the end of the arc, so leave him alive?" The anime has its myriad of problems, but very, very rarely would have they directly changed something like this. It's a very odd decision for them here. If they didn't know what happened- just leave it open ended like Oda actually did in the manga. Not this.