Chris, I don't mean to put words in your mouth, but I think you meant apathetic instead of cynical. Cynical is more distrustful of others (ie Hachiman f/ SNAFU) while Sakuta just seemed more aloof to his surroundings stemming from his social standing within the school. I never really saw him that cynical in the various situations. I guess he did come off a little annoyed at times, but I think that is pretty understandable given all these strange occurrences kept happening to him. He's only human right. If he didn't care, he wouldn't have been so patient with the girls. I guess you were too focused on all the cute girls though.
Sidenote - I really loved the fact that Sakuta wasn't the white knight who had to solve all the girls problems (except for Mai), but allowed them to come to the solutions themselves. All he had to do is be there for them. So wonderful.
So I agree with Andrew in that Sakuta definitely cared for each one of the girls in his own way. It just wasn't to the level of Mai, which to me, is a wonderfully refreshing take on this harem(ish) show.
Definitely an interesting take on Sakuta being the catalyst for Kaede, but if I'm being honest, I really hope that is not the case. I honestly think your reading too much into the supernatural element of the show.
My take is simply that Kamoshida-sensei is using the adolescent syndrome as the visual representation of Japan's high societal pressure on it's people which is twice as much for high schoolers dealing with societal pressures as well as social pressures. So each of the girls deals with an aspect of those pressures: Mai = public, Tomoe = social, Futuba = self, Nodoka = family.
Which brings us to Kaede. She is also social, but with a focus of bullying. While obvious, it's a big topic in the world so I can't blame Kamoshida-sensei for going with it. But as for Sakuta being a catalyst, I don't see why his pain of seeing his sister being bullied manifest in Kaede being harmed. It could be an unintentional consequence, but as they stated with the “body swap” of Mai and Nodoka, that wouldn't have happened if Mai didn't have some type of unresolved issues with Nodoka as well. I really think Sakuta was just around for Kaede's adolescent syndrome. If anything Kaede's responsible for Sakuta's episode.
I just think it wouldn't fit the down to earth characters to have the main character be so important to this story as being able to manifest syndromes in others. I really like that Sakuta is just the vehicle in which we view the stories. It is a little convenient that all these syndromes happen to one individual, but all stories are convenient, and I think the convenient idea is the most compatible one.
As for Shoko, It definitely involves Sakuta's subconscious, but I wonder to what extent? I think Young Shoko is significant because everybody acknowledges her, so I question if Shoko is entirely Sakuta's subconscious. I can't wait for the movie to find out.
It's just my view point and I most certainly could be way off base, but regardless, I really did LOVE this show.