Madras used susanoo without any eyes
And yet we still debate on exactly *how* he did that because there was no explanation.
Itachi- "The power that awoke within these eyes that fateful day, the third power, Susanoo".
Key words: Within these eyes.
Sasuke- "Only those that control the double Mangekyo can achieve this power" -Stated after revealing Susanoo.
Key words: Control the double Mangekyo.
It doesn't necessarily matter for something to be "understandable" for it to be considered an asspull. People are getting powers left and right here overnight.
Realize that we are the night of day two in this world, so Naruto's "yesterday" was him literally at the Island Turtle learning to control the Kyuubi's chakra and then fighting Raikage and Tsunade (if you call that a fight). Now, he would shit all over his past self from a day ago.
Same thing with Sasuke more or less.