No he observed him with sharingan and after the observation he thought " so this is what he is like .... chakra" .
From a perspective of a normal eye user, tsunade said "this form.... naruto"
Your point was that they observed the same thing which would mean sasuke was seeing the same thing as tsunade and didn't activate sharingan to see naruto's chakra.
But i have shown you what they thought was completely different unlike what you stated.This further strengths my argument that sasuke activated his sharingan to see naruto and his chakra flow (or whatever he can see with sharingan) .
Madara's susano will not be as strong because he needs his eyes to use it at full power. But what doesn't make sense in your theory is that why is he able to use only one technique?
Even one rinnegan is enough to use all the six rinnegan techniques, this is the hole in your theory.
You should realize, if you suggest eyes are necessary for use of ocular powers, then both of the eyes should be accessible by madara to use susano, with one eye , he should not be able to use it. But what he can do with one eye is use all 6 rinnegan techniques.
BUT according to your theory, he is linked to only one of his eyes and still can use susano which requires two eyes and cannot use rinnegan technique which only require one eye. Also, if the connection is not that strong this means he can only use one technique right? so he should be able to use any one technique at one time but noo he is only able to use susano. Susano and susano alone.
So do you get it now? your theory have holes in it and does not explain many things, instead raise nothing but more questions.
Feel free to justify the holes i pointed out, i will be happy to debate further on this theory.
Now comes this itachi thing.
i have re-read the chapter involving itachi and sasuke.
Here is my observation :
itachi :
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You can see his eyes looks like normal eyes just his eye ball seems smaller. The fact that he can use susano means he is still not blind and if that is the case then we should be able to see his MS , but not even 3t sharingan is seen.
This is because itachi used susano without sharingan.
Now let me show you sasuke right before he was blind :
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As you can see, right before he was blind, his MS can be seen.
But in itachi's case we cannot see his MS.
And after sasuke got blind :
You can see his eyes go full black, sharingan disappears and susano as well.
So let me recap what we observed.
Itachi is using susano without sharingan activated.
Sasuke is using susano with sharingan activated, he goes blind, his eyes go full black and susano disappears.
Right before sasuke got blind, we could still see his MS but that is not the case with itachi, we see normal eyes.
this means itachi used susano without sharingan activated and he was not blind, he was near blind.
So yeah, itachi also used susano without sharingan just like how madara used it.
Madara can control obito and make him do rinne tensei through black zetsu and chakra rods but he cannot receive chakra from it.
look here :
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madara needed to have physical contact to receive chakra from hashirama even though black rods were implanted in him.
Explain this.
Since he can't receive chakra, eyes being connected to zetsu and usage of susano is impossible.
Even then this explanation has hole as i said above,
1. 2 MS are req. to use susano.
2. Even if he can receive chakra, its still too far fetched to believe that chakra connection have enabled him to use his eye technique.
3. Why only susano can be used and not other rinnegan/EMS techniques?