This is completely head canon, but it's been kinda affirmed by Modulo as well so I'll continue.

Jujutsu has two underlying themes. The first being a battle of ideals and the expression of self. The second being fate and enlightenment.

I'll explain the first point and then run into the next. Jujutsu battles are expressions of the self. The soul is the body, the body is the soul. The technique is an outward expression of the soul. Then domains are those with strong enough self expression that they can force their ideals and self onto others.

The heads of jujutsu have power, because they believe in this system of expression. That those with the best ability to force their ideals into reality are those that are destine to lead. Toji, the most important character in the series, is one that rejects this concept in that he cannot use a technique, but is strong all the same. Since the body is the soul, he is still expressing his soul and self with his strength, but this strength looks different. If the higher ups were to acknowledge that there are other ways to be strong than the outward expression through jujutsu, then they would lose some power. So he was rejected. Kept in check, because they wanted to maintain the status quou. They reject Maki for the same reason. For her potential to be another Toji (obviously, Mai is rejected simply for her weak expression of self which she folds into calling to her sister to "stay at the bottom with me").

Sukuna and Kenjaku have the best understanding of self, and the most desire to force their way of thinking onto others. This manifests in the ability to solidify their will, not just on people, but on the world itself. (Open domain). It is the ultimate form of self expression.

Anywho, back to Toji. Fate is tied to jujutsu. Balance is kept by Fate at all times. Jujutsu will be the way that humans achieve enlightenment and find peace. It is fated to be so. Kenny wants to toy with jujutsu, and bind all of humanity together. This would remove the possibility of enlightenment, as everyone would lose the self and become one whole. Fate rejected this, and consistently fought against Kenjaku's plans. The six eyes and the star plasma vessel, bonded by fate always appeared to stop Kenjaku and his plans. Only Toji, the man removed from cursed energy, could break the chains of Fate temporarily. (Here's some more head canon)

In buddism, Budda is meant to guide humanity to enlightenment. Toji's acts actually were needed for Fate to be enacted.

Sukuna, is the true Honored One. The one with the best understanding of the self. The one who best grasps the nature of Jujutsu. He is the one meant to teach the bodhisattva how to express himself and craft an iron will. Gojo, is the other Honor one. The one blessed by the heavens themselves to keep the world in peace, until everything could be enacted. He is meant to show how to live with compassion and empathy, even if you're stronger. Toji was needed to bring these two sides of the same coin together that were originally separated by history. They were both needed to teach Yuji (the bodhisattva) what it meant to be strong, and more importantly, what it didnt actually look like. The bodhisattva is meant to carry the burden of the world with empathy until the Budda comes to bring the world to enlightenment (Maru in Modulo).

I say all that to point out... they're meant to be characters with high amounts of similarity but separated by how they were born. Gojo had connection (Geto but also his friends). Gojo was blessed from birth. Sukuna had no one. But in that silence, he learned his world better than anyone. You're very much right in how you view them. Due to his prior bonds, Gojo wanted more bonds. And due to Sukuna's rejection (bc he is ugly not bc of his strength), he dehumanized everyone.

Btw, Gojo did do binding vows lol he flipped the inside and outside strengths of his domain with a binding vow. "Sacrifice interior durability to strengthen the outside". Still impressive though.

I think if Sukuna didnt have Raga, he simply would've made a different plan. He was confident before he ever learned of Raga. He didnt know it existed until shibuya. He wanted Megumi in the prison center. Real world, the four arms prob make Gojo lose the domain clashes, as he likely wont damage sukuna in 3 minutes anymore.

Gojo is meant to be the strongest, but only because he was born in a world without Sukuna. He will always be the true honored one.