Kurama merely noted the feel of his chakra reminded him of Madara and I'm certain he was able to make this distinction not because their powers were close, but because both were reincarnations of Indra.
Uh? "Eyes with such power and chakra even more sinister than my own" He's definitely referring to power, partially.
Its not that I think Madaras chakra should be stronger and more potent, the manga portrays it to be that way. The manga portrays everything about Madara to be > Sasuke.
The manga portrays that Madara is all around stronger than Sasuke, it doesn't imply that Madara is better than Sasuke in everything, nor does the manga imply that Madara's chakra>>>Sasuke's chakra.
Orochimaru mentions Sasuke could surpass Madara. Tobirama mentions Sasuke has the potential to be even greater than Madara. Obito said it too (Not sure if he said Nagato or Madara I don't remember). With these statements the manga is portraying Sasuke has not surpassed Madara yet but when he reaches his prime he most certainly would.
That was all before EMS Sasuke showed us his PS. Naturally Oro would say that he could surpass Madara, but hasn't yet, because his best was a Senjutsu Susanoo.
Since we discussing their chakra in this case, all of Madaras Susanoo versions were bigger, stronger, more durable, etc than Sasukes.
Bigger? Sure. Even with Rinnegan they still are. Not really relevant.
Stronger and more durable? What suggests that EMS Sasuke's Susanoo at their best aren't as durable as Madara's at their best? Or at least near it?
Madaras chakra was large enough to duel Hashirama (even SM Hashirama) and both ended in the same exhausted state. EMS Sasuke can never achieve something even close to that level and he certainly can't last with Hashirama for 24 hours.
Hashirama used way more chakra than Madara did. Hashirama had to consistently create Bijuu Sized+Mokuton constructs, and control them to fight against Madara, who only had to use PS briefly since Kyuubi has his own chakra reserves, and added much more firepower to his arsenal w/o Madara having to use excess chakra.
As for the 24 hours bit, you don't know how what Madara did during that fight to say that Sasuke can't last that long as well, but I doubt he could as well. Not really relevant though.
Nor is chakra amount=/=chakra strength.
Sasuke attacked and Naruto defended. That does not mean if Naruto attacked with his tails that Sasuke would be able to defend against his attacks, especially since one tail was all that was needed to stop PS slash.
Sasuke attacked, and Naruto counter attacked. He wasn't guarding, he was parrying, which makes the whole comparison valid.
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Was Naruto holding back? Yes. Was he the one engaging Sasuke? No. Does that change the fact that he did attack? No. Does that change the fact that their avatars are shown to be physical equals? No. Subtract Rikudo Power and you have Sage Kurama Avatar=Perfect Susanoo in speed, strength, and durability.
This was the entire gist of my earlier post (not sure if you read or not). I'm not saying EMS Sasuke can't use PS anymore, I agree that he can, but he would need immense chakra to reach the large form Madara used, chakra levels he does not have so his PS would naturally be inferior to Madaras and its most likely the reason the difference in their V4 are so damn drastic:
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Madaras tanked a Bijuu Dama and the one Sasuke used certainly isn't replicating that feat so its clear Madaras is much stronger, not to mention it looks about half the size of Kurama so its way larger than Sasukes. To give an idea of the size difference between them, that Kyuubi BD is bigger than Sasukes v4, then the same BD is much smaller than Madaras v4.
Not really a fair comparison, to take Sasuke's V4 Susanoo at it's smallest and then compare to Madara's. V4 Susanoo at it's peak is a full bodied Susanoo, which then becomes PS. As Madara has shown us, it's around the size of the Perfect Susanoo, just not stablilized, thus Sasuke can clearly make a much much larger V4 than what he showed us after he had just gotten EMS.