Surely you have your rights, but I can't see it like you do. I have a feeling that you try to present Kyon's submission in somehow 'bdsm-ish' terms. But it's not bdsm story, or rather I don't think it is. You're right, Kyon can go away in any moment and he still chooses to stay. But I think that this is precisely an evidence that he's weak. Even if there is a power exchange, there still has to be some respect to other person. Lucaon has no respect for Kyon, treating him like a thing for his sexual release. As I said, it's not bdsm - they don't have any sort of agreement and Lucaon doesn't care if Kyon 'like it rough' or not. Kyon knows he's not loved or even respected and he knows he's being used. He claims he's in love with Lucaon knowing almost nothing about him, which is pretty stupid. I, as a submissive myself, can't understand Kyon at all. I think it's just a common sense to know if a relationship is healthy and if another person deserves your submission, because submission is a gift. I think that only weak person would choose giving his/her submission to someone like this, who treats them like a trash. But, well, maybe it's just because of my character and personal life experience that I see it this way.
Not everyone will see it as I do, and not every role chosen is necessarily sexual. I think some of what I see in erotica reflects relationships that would be very unhealthy in real life (especially for BDSM erotica) but that I personally choose to suspend disbelief about certain aspects of the person or the relationship when I think it is part of the story. I do see aspects of this story as BDSM erotica (though not a model for real life BDSM relationships). But my main point is more than just sex. It's about choices and different types of strength.
You may not agree with Kyon's choices, but he did make them. There are many yaoi stories where the relationship starts with one person, usually the uke, being trapped or tricked in some way (your family/organization owes money and you must pay with your body, you have to do this because....). Sometimes the sex itself is pretty vanilla, but the weak character is just cute and stupid and mostly useless. In this case, Kyon thinks, acts, and pursues his goals. He chose it--in fact he was the pursuer of the relationship. You may not be able (or willing) to suspend disbelief and accept Kyon falls in love so quickly (or based on such a brief past connection and belief in who Lucaon was). That's fair. But I think the story presents this as something Kyon wants, not something he is forced into. If you can accept the premise that this is rally what Kyon wants, then he is still strong to go after it and not just a victim.
I may be splitting hairs, but I see a difference between a weak character and a character who chooses to take on a submissive role. To me, weak characters are those who let themselves become victims again and again, and do nothing but look cute and pitiful even though they don't seem to want to be in that situation at all. Weak characters are usually also stupid and easy for anyone to manipulate--and they tend to have a 2-dimensional quality where they fall into the damsel in distress trope. On the other hand, there can be characters who choose to be submissive or who have strengths such as perseverance and compassion that make them valuable and not just "cute and stupid". I realize "compassion" without actions to back it up can go with the weak characters too (and I still think "heart" is a crappy superpower), but if it is done right, a charter who is submissive can accomplish much and reach his or her goals instead of just being a pawn and a victim all the time.
In this story, I think both Kyon and Christoph choose submissive roles, but each has his own agenda (though Kyon is less experienced and therefore a bit more innocent). No one forces either of them to be the servant and hover around their master--they each want to. It's choice of role, not a general weakness of character.
Christoph sometimes bullies the master into doing what Christoph thinks needs to be done. In the face of conflict, Christoph says things that sound very submissive--but he actually diffuses dangerous situations and gets what he wants without useless confrontation. When there is an explosion, a master needs to shield Christoph, but in day to day life, Christoph shields his master and keeps the place functioning. I think Christoph is actually very strong and sometimes wiser than Karis.
Kyon is in a slightly weaker position whenever Lucaon is around because Lucaon is his weakness--so to speak, but Kyon chooses to be a servant and stay a servant and Kyon actually pursues Lucaon through the story, if you pay attention. Kyon gets what he wants (though perhaps he should want more). Kyon didn't fall into Lucaon's trap--maybe Ryan manipulated some things way back (I am not sure), but Kyon applied for the job, Kyon repeatedly made attempts to be closer to Lucaon even when Lucaon pushed him away, and Kyon stays no matter what Lucaon does. Kyon may not know everything that's going on or have experience with fighting, but Kyon is not stupid. Kyon is generally competent (especially when Lucaon isn't round) and Kyon faces difficult things and does his best. He isn't a slave or in an unbreakable contract. He isn't falling for some stupid BS line. He isn't helpless or a victim. He just takes on a submissive role with Lucaon--and it's possible he enjoys being submissive. Regardless, he's doing it to get what he wants (Lucaon's attention and trust). He's not being forced into it because he is weak. There is a strength to his submission, if you look for it.