I mean that does make sense. And obviously we've seen Madara use susanoo with Rinnegan and obviously he's using it with no eyes. So if this is true, then I'm curious as to why we havnt seen anyone use susanoo with 3 tomoe Sharringan. It doesn't really matter, but just sayin...like if MS/EMS ends up exhausting chakra/eyes, couldn't you use susano in 3 tomoe state to preserve chakra? Only then activating MS/EMS when needing to use a jutsu?
This^
I was thinking the same thing. That is if this can be achieved by any Uchiha with MS or EMS. If that's the case I would think Itachi would have used Susanoo in regular 3 tome Sharingan form since his stamina is weak and he needed to conserve chakra more than anyone else. But I am thinking this is something unique to Madara. As you know each MS Uchiha has something they specialize in beyond the other members of their clan.
Itachi-Sharingan Genjutsu (Tsukuyomi, Koto Amatsukami, Izanagi, Iganami)
Obito-Kamui
Sasuke-Amateratsu (Enton jutsu)
Madara-Susanoo (Perfect Susanoo)
I think since Madara has mastered Susanoo past the others he is able to use it without possessing the MS, EMS, or Rinnegan. He is just on that level I suppose. just a theory though.