@Underlined, clearly you don't know what adaptation and evolution of an organism is. Do you know what adaptation or evolution is? It's when an organism adapts depending on the nature they live in. Now, turn this biological fact into a Chakra term; this is what you get:
No matter how many times you try to deny, Indra's Chakra and Ashura's Chakra have kept on adapting and evolving inside Madara for years. When Madara took Hashirama's cells (Ashura's Chakra), he was already young. When he awoke the Rinnegan, he was extremely old.
Now, between the time-span of the two events, the Chakra of the two brothers must have kept on adapting and evolving in nature, quality and quantity in order to reach Hagoromo's Chakra. Otherwise, it wouldn't have took Madara almost his entire life to awake the Doujutsu compared to Sasuke, who was given the original Chakra, whereas Madara needed to adapt to the original Chakra.
The fact of the matter is the Chakra of Rikudou's inside Madara was so much large, that it ended up giving him the same Rinnegan as Hagoromo compared to Sasuke. And as Hagoromo said, Madara has his Chakra and its power:
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That's not how SM works. Senjutsu = Physical energy + Spiritual energy. Madara's physical energy (Ashura) + Madara's spiritual energy (Indra's) + Senjutsu = Rikudou Senjutsu.
@Bold, argued before and disproved. Fan-fic theories don't coincide with the manga.
@Italic, countered above.