oh, oh, oh, but i liiiiike this — you know that theory about how, Zuko, Katara, and Toph are each crazy-powerful, especially given their respective ages (like, Katara and Toph are literally unparalleled in their field despite being so young, and sure - in terms of Brute Force - Zuko isnt as strong as Azula, but he is unquestionably the better bender of the two of them, not only in his ability to redirect lightning - an insanely difficult thing to do - but also just in his overall understanding of the element of fire) and that the three of them are their respective element’s chosen champion; their element’s answer to the fact that the Avatar was absent for 100 years. That each element is trying to fill the vacuum left by an absent-Avatar, and they each have picked one champion to fill that void, and those champions are our three here. That the three of them together make three-quarters of an Avatar. That the world was trying to create balance by gifting extraordinary abilities to three non-Avatars, who - if they worked together - could maybe bring the balance that the Avatar was supposed to.
Well the couple of versions of that theory I’ve seen either don’t account for the Spirit element of the Avatar, or say that Iroh is the Spirit’s representation, which… works, I suppose, as he certainly has a great respect for and understanding of the spirits. But as OP says, he has to work very hard for any actual encounter with them. And it breaks pattern, because the others are all of a similar age to each other, whereas Iroh significantly older and also not a core member of the Gaang.
Our boy Sokka just strolls into situations with Spirits on the regular. He finds himself tangled up in Spirit related bullshit all the time - which is hilarious, given how scientifically-minded he is and how disdainful he is towards “spirity nonsense,” and I confess I’ve always just seen it as that. Easy comic relief. Get the scientific guy tangled up in intangible, spirity shenanigans, how hilarious would that be. But what if it’s more than that?
No one else has just…. falls into Spirit shenanigans the way Sokka does, or has encounters with Spirits the way Sokka does. Even Aang objectively has a harder time getting in touch with Spirits than Sokka (unwittingly) does, and not only is Aang the actual Avatar, but he’s a monk. They're known for their spiritual enlightenment.
But Sokka just…… crashed straight into the Avatar’s ice-ball, and he not only fell in love with a girl who was part-Moon Spirit, but she fell in love with him too. Sokka was the one who spotted the Wan Shi Tong Library in the desert. You know - the literal domain of the Spirit of Knowledge. He’s the one who decided to go there, and then he just… found it. This library that’s so hard to find that many scholars believe it’s just a myth, he decided to find it and then he did. Just spotted it out in the desert. Just like that.
Sokka got kidnapped by Hei Bai and just…. chilled out in the Spirit World for a day. The Spirit hallucinations talked to him in the swamp – the only one of the Gaang who was actually spoken to by them. I feel like there’s other occasions, too, of Spirity Bullshit befalling Sokka, but I can’t remember them off the top of my head. But none of the others have this many interactions with Spirits, and certainly not accidentally. Aang has to seek them out; they don’t really just happen to him, not the way they Just Happen to Sokka.
So what if, what if, what if…. What if Sokka is the Spirits’ answer to the lack of an Avatar. What if Katara, Toph and Zuko represent their respective elements, and Sokka represents the Spirits. What if Sokka is the Gaang’s bridge to the Spirit World.