Theory:Susano'o is the Juubi's yin chakra

[Opiuchus05]

The sage ate the fruit from the god tree(juubi)giving him strong chakra,body,and rinnegan
Chakra is physical energies+spiritual energies

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the older son only inherited his spiritual energies;the sage's spiritual energies+the older son's physical energies=a yin chakra because the spiritual is more powerful than the olders physical,this also made the rinnegan some kind of swirl pattern

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his yin chakra got weaker and eventually came the uchiha's but they have power ups to get to his power
tobirama said that a special chakra sprouts changing the sharingan into mangekyou sharingan

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and tobirama said that hatred makes a uchiha more powerful

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when sasuke used his susano'o for the first time his chakra was like genjutsu which is the yin element

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and hatred made his susano'o grow even more
against danzo

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and against kakashi.karin said his chakra got colder

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he gets itach's eyes and feels his power flowing through him

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Madara and sasuke both represent older son and only known uchiha's to have ems, last powerup before rinnegan, also both have perfect susano'o
the more their yin chakra got closer to being like the older son's the bigger susano'o was
the older son's yin chakra comes from the juubi's
madara doesn't have his eyes anymore but he still has the juubi's or older son's yin chakra

 

[-immortal-]

nonon.. susano is the power of eyes.
well we seen its not needed with eyes nomore

 

[-Sky-]

The very first sentence of your post is incorrect, his mother ate the fruit not him.

Regardless, all Chakra came from the Juubi so you're probably right in a sense.

 

[Bimbonium]

Sasuke is yet to show PS.