What we can conclude is that Susano not only has different stages of progression, but for each user it also has access to different abilities. Itachi's Susano was unique in that it had two one of a kind techniques that are not unique to Susano. They are actual techniques that are passed down from teach to student, and Itachi somehow managed to learn both and keep them safe from the rest of the ninja world.
In addition to that, his Susano was fully formed and capable of wielding those techniques (much like Madara's Susano was capable of using techniques and weaving signs). Was it invincible? It certainly appeared that way to any ordinary ninja. I think that is part of the perception of the characters more than it is written that way by Kishi.
Sasuke's Susano only became fully developed in his fight against Danzo and then Kakashi, where he nearly went blind due to over use of the MS. While Sasuke's Susano doesn't have access to the same techniques that Itachi's did, it does now have the full cloak/armor set and techniques of it's own. Being able to manipulate the black flames and fire a long ranged attack are very formidable techniques.
Aside from that fact, Danzo was only able to penetrate it before it became fully formed. It was still in the early stages where it was missing it's cloak/armor. Danzo had to use an enormous amount of chakra to summon the nightmare devourer and then use wind techniques to even put a dent in that Susano.
The point being, that not everyone is a 'fanboi.' Some people actually pay close attention to the entire manga series and don't make assertions about who's stronger or weaker in a certain match up. I may or may not like any of the characters, but I can tell you right now that Sasuke and Naruto have been in a constant rivalry to develop their abilities as much as possible since the beginning of the manga.
The entire story is a culmination of revived war and hatred in a world where Shinobi are tools to be used for war, and the focus of the story is about how those ninja deal with such a world. It's not about who's cooler or who's stronger. It's about who uses their abilities in the most efficient/effective manner, and the impact that has on the storyline.
Madara's abilities are not yet fully known because he's only been summoned by Edo Tensei for a few chapters. We still have an upcoming battle between Tobi, Naruto, and B. We still have another upcoming battle between Itachi and Kabuto. Putting all this thought and conjecture into Madara and Susano is largely irrelevant.
Susano is a tool to be used by ninjas, and so far Edo Madara has shown unparalleled offensive capabilities with his Susano, which has not been fully formed yet. Whether or not he can form it to the level of Sasuke or Itachi is irrelevant. Madara hasn't been sealed yet, so there is still the possibility that he just hasn't done it yet.
Stop speculating over trivial BS plz, it's annoying.