You're right that part where we could see this coming a fair way off. Weeks or months ago, we were all speculating that Kaguya would be the final antagonist, and in order to power her up accordingly, she needed to nick Madara's power. Madara was, after all, instructed to consume the tree, so he did; he was already digging his grave at that point. The problem I have with this is ...I didn't like how Madara basically got betrayed by Black Zetsu that was weak, imo. I would rather Madara getting his ass kicked before Kaguya took over...like Madara vs Sasuke and Nartuo together like how they come up with strategy plan to defeat Madara.
If Sasuke and Naruto killed Madara and Madara failed Kagyun's wishes so somehow Black Zetsu took his corpse that's where Kaguya takes over and clean up Madara's mess. That would been much better, imo.
If Sasuke and Naruto couldn't beat Madara while Kaguya is much pretty much very stronger than Madara but we all know it will be lame how they will be ended/sealed Kaguya. I don't want to see weak ending, hopefully.