Oh shit I can't believe I forgot this statement until now.
うちはマダラ、うちはオビト、 そして尾獣の集合体である十尾の復活・・・!!畳み掛ける様な敵の猛攻に、 ナルト達は忍史上最強の術 "忍連合軍の術”で対抗する!!
This might not apply to techniques that hadn't been introduced yet like the Shinsuu Senju or Deity Gates, but this should definitely mean that the Kurama amped Alliance>Edo Madara's Perfect Susanoo which had been shown prior to the Shinobi Allied Forces Technique. So uhhhhhhhh since PS>BSM Naruto, MKCM2 Naruto doesn't really scale to the Juubi, it's just that Kurama's chakra is a non-linear amp. Still don't think 50% Kurama scales to him, but MKCM2 Naruto probably needs a downgrade regardless.
Edit: Damn the databook says it too. ナルトの援護に忍び五大国の強者が集う! これぞ史上最強の忍術なのだ。