We all know that Uchiha Madara was defeated by Shondai, long before the Naruto story takes place.
I was going through the old mangas, noticed a thing and another, puzzled the pieces together and came up with another evidence confirming that Shondai is more powerful, or at least had greater potential than Uchiha Madara.
Here Hatake Kakashi confirmes that Uzumaki Naruto's chakra potential is above uchiha Sasuke's.
So Uzumaki Naruto's chakra potential is greater than Uchiha Sasuke's. Of course the effectiveness differs depending on what jutsus one's capable of. But going by potential, Uzumaki Naruto is likely to surpass Uchiha Sasuke.
Naruto's potential > Sasuke's potential
So what does this have to do with Shondai and Uchiha Madara?
Well, when Hatake Kakashi was chasing Uzumaki Naruto and Uchiha Sasuke in the retrieval arc. He said that they were much like the ninjas that fought there before, in other words Shondai and Uchiha Madara.
You can scroll back a few pages after you've klicked on the source (link at picture.)
Kyuubi also sees the similarity between Uchiha Madara and Uchiha Sasuke.
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With this one can conclude that Uchiha Sasuke's potential is similar, at least relatively close, to Uchiha Madara's. And Naruto's probably similar to Shondai's.
Uzumaki Naruto's potential > Uchiha Sasuke's potential
Shondai's potential > Uchiha Madara's potential
Shondai's power > Uchiha Madara's power
Of course this is very far fetched and vague, and shouldn't be given much credit or be taken to heart. I just thought that I might post it, since I noticed it. 