good post
I just want to add that kishimoto said madara has no weakness while everyone else has (this means only madara in NV has no weakness), so how do you defeat a person with no weakness.
madara was restricted so much that he never used the same jutsu twice, and never using his complete arsenal and never taking his fight seriously since he has his goals to complete and when he came to fight seriously kishimoto used BZ to stop him and used kaguya instead.
obito used the juubi and used the rinnegan and said the rinnegan itself was too strong and almost lost himself and stated just dual rinnegan madara is unbeatable.
you probably remember when naruto and sasuke came back with hagoromo's power naruto said that he's not going to fight madara alone but with sasuke, so he himself believes 1 rinnegan jj madara was too much for him so that's why he stated to won't be fighting alone.
Hagoromo say kaguya was the strongest he describes her power based around the rinnesharingan and madara has this eye aswell. Madara should beable to use the eye since he awoke the eye himself and used the I.T which proves he can use kaguya eye the he himself awoke.