-Ok We All Know the Sharingan Perks....Like Tsukiyomi, Amaterasu, copying Justus,and Taijustu, but this is its Biggest Perk....Which was use against Kurama Many Times Mind Control
Obito even Showed that against Many Tailed-Beast at One Time with Only a 3-tomoe sharingan.
Now Hear Where Plot Armor Comes in at: Naruto and the Kurama Switch bodies more than once Now Between The Obito fight and when Madara came into the Mix...plus Bee did too with Hachibee
My Guess if they (Obito or Madara) use the Same Mind Control Move like they did to all the tailed Beast in the Past
wouldnt the Fight Be Over Now...I mean: 1-Killer Bee Would Be Dead By Now we Seen What Sasuke did to Him
2-Kurama and Hachibee Should be under the Influence of their Genjustu
3-The Story is not Using all of the Sharingan Powers to full extent
Now with that Said We Know the Sharingan Is Capable of putting Even Tailed-Beast under Genjustu its also know that With Kushina and Obito in the Past it Can be Place on the inside of a Host to
Cause Obito did use the Genjustu to restrain Kurama in the First Place....then Setting him Free to attack Konaha.
I think its Plot Armor Because Logically...Nothing Should be able to Beat the Sharingan if Use by the Right Person like Obito and Madara or Sasuke