What's their deal anyway?
I have absolutely fuck all when it comes to knowledge on that part of the Nasuverse
Basically it's heavily implied Soujuuro came into the same school as Kuzuki...
Now to say why that's important, I have to go back into how the Nasuverse actually works in a sense.
You know how we call Kojirou and Musashi Sword Autism right? If you primarily stay the hell away from Human Society where rules and otherwise would stop you from doing bullshit, you can potentially do things that are impossible for humanity to ever do normally... provided you stay away from Human Society.
After awhile, Kojirou(or one of the conglomerate that made him Kojirou... there is no real Kojirou Sasaki in the Nasuverse anyway, FYI) basically practice trying to cut a Swallow and his Tsubame Gaeshi for basically his entire life... and never stopped trying until reality literally gave up and gave him his Tsubame Gaeshi... basically days before he died.
To put it back to Sojuurou, he basically was trained so hard that the limits of the human body was just GONE. He could legit do impossible things in the past and was a complete monster...
But when he made it to Human Society, that got weaker and weaker because he understood the rules of what he can and cannot do.
That's how Nasu graded them, Sojuurou would canonically be the strongest at his maximum but he would have to stay away from Human Society to do so, otherwise, he would be like Kuzuki to where he's Superhuman but that's it.
