When it comes to skill ryuunosuke takes it beyond understanding. I think you're forgetting yuji is in his 9-A key so he doesn't have the skill adaptability he'd have with his higher tiered self as he just became a sorcerer. This yuji is inexperienced and while has adaptability, he has never adapted to someone with 300+ Years of experience in this key and he fought this character and did well without his precognition coming into play, even dodging attacks like echo which attack reflects his opponents with the same speed and force back at his opponent, (he did this at point blank range, multiple times). Yuji also has action mimicry which lets him copy the movements of others after seeing it once to counter it. This being said yuji gets outskilled and out maneuvered easily by ryuunosuke. i also think youve ignored again why itadori will NOT touch ryuunosuke, his senses allow him to detect others who use stealth mastery which works on well profound hunters. And his precognition which lets him see attacks two seconds ahead and using his agility to evade said attacks which we can conclude ryuunosuke is more agile than yuji seeing his feats against echo. Along with his acrobatics pf being able to twist himself midair to dodge repeated sniper rounds and danmaku from shide which can encompass tens of meters and have piercing damage. The stamina argument is not convincing, shinpei has witstand being able to take worse injuries and pain more than yuji and still being able to fight. He also doesn't feel pain at all as he's a shadow (check physiology page) and although one hit from yuji would be detrimental, i already argued why he will not touch ryuunosuke in the first place.
So firstly, Yuji has cursed energy in this key. He's just not able to use it very well. Secondly, Yuji's adaptability in skill to others isn't reliant on cursed energy. That's an intelligence thing, something unrelated to all of his keys.
And having 300+ years of life experience doesn't equate to having 300+ years of combat experience. Shibe has been hopping and swapping bodies for 326 years, we don't know how much of that was fighting so that's not really a good example of either his fighting skill or experience. And more importantly, Shinpei or Ryuunouske don't have this 300+ years of experience either, they just fought someone whose been around that long.
Experience isn't the angle it's being made out to be here.
And when I'm talking about stamina, I'm talking about how long a character can fight period. How long Shinpei and Ryuunosuke can keep up a high intensity battle even without getting hurt. All of their stamina feats you've brought up are more about how much damage they can tank and keep going. They don't appear to have any, so unless you got something like Shinpei and Ryuunosuke able to fight for long stretches of time, I don't see him having more stamina in the sense of how long he can fight than Yuji.
And if he starts tiring out before Yuji does, then it doesn't matter how much more skilled he is because his speed and strength won't be able to act upon this skill. Yuji
They don't. Data in STR includes memories, mind and the data itself. Memories and the mind empower shadows data which i could get more in-depth in, (read physiology page) but they do not work the sane at all. Sukuna would need to be able to interact with the data as shide could to supposedly rid ryuunosuke from yujis body.
Information in JJK, also includes memories and minds and even includes souls. The abstract nature of Shadows is also matched by the Abstract nature of Curse Spirits who are made of information as well. Information in jjk can also be used to create copies of people like how Shadows work in Summertime Rendering. Data in STR is very similar to Infromation in JJK, so Sukuna most certainly should be able to interact with Ryuunosuke.
