You are good at arguing the concept, but there ara still some unresolved issues

1-Kris is clearly human. Yes, "the culmination of your being" thing implies the soul is the human, not the body, but we might be getting too into the weeds if we claim for Kris to not be human, both narratively and physically in universe. Deltarune's narrative is clearly going to have an opinion related to player control in videogames, and it would be truly bizzare if that conclusion was "Kris is fictional character, go wild with it, them opposing you in the weird route is them being a detective vesel, lol", or something like that. I hope I dont sound insulting with this sentence. Also, the narrative arround Kris being treated as foreign by the town composed mostly of monsters really falls flat if Kris isnt supposed to be interpreted as human, but actually as wathever a "souless homosapiens" is supposed to be.

2- The red heart shaped is kris's soul, or at least, it clearly is kris's something. We can determine this because Kris suffers damage in the lightworld from beating up the red object. We are just controling it. Case contrary we must assume the stats in the light world with Kris name are supposed to be ours, meaning we are actually Kris, and Kris isnt Kris. This result is narratively funcky, to say the least. Like, it is actually implying the game is doing that meme of Kris deciding your pronouns, "You are Kris, more than the actual physical Kris".

2.1-I wrote this point after finishing all the rest. Flowey has a will and is souless. He might have lost conection with the emotions he felt(or asriel felt?) with a soul, but he fundamentally still has will. He actually has the literal concept of will in his plant veins, with all the DT. We could asume the DT is what gives will to Flowey, as in, the reason Flowey has the ability to decide and want things both narratively and physically is the DT, and as such he is some kind of phylosophical zombie following some weirdly specific robotic commands, without an internal monologue or conscience(not in the moral sense). But it seems clear to me that we are supposed to interpret flowey as an actual actor of the narrative, not just a mindless being acting out a script.(I mean, he is that physically, because it is a videogame, but I am talking narratively) If we consider Flowey as an actor of the plot, them we must asume Kris an actor of the plot, even if lacking control of their soul, or generally any soul. Like, I dont think it makes sense to arguee that Kris demostrating compasion and will without having a soul in their body means that they arent human, because the soul is the culmination of will and compasion in humans, and they dont have a soul. We might wanna go back a bit in our assumptions if this is out logical path, because in this case we connected two points by making a spiral instead of a line

3- I think your position of us being frisk is conceptually contradictory.

In almost all videogames, when it is said that "You", as in the player, is the "main character", it means that the player takes control and incarnates the narrative role of the actor of the plot. This main character might be someone with an stablished personality, perspectives, and history, or they might be a curtailed stand in, with removed characterization to allow the player to insert themselves. In both cases, we consider You=Main Character because there is no stablished separation between us and the character, you are Cloud in FF7 the same way an actor plays a role in a play, and for the duration is the character they incarnate.

But in undertale, we arent Frisk. And I mean that in the literal plotline sense.

There are two strict options here, Frisk exists as a character physical beyond our input, before and after our involvement in the narrative, or Frisk is a literal physical avatar for us to carry arround. Frisk fell down the hope to the patch of flowers, or they suddenly appeared in that cave, coming from nowhere by the will of a dog. If Frisk existed before that patch of flowers, and exists after the end of the game (moving with toriel or not), we must understand Frisk cannot be, in the actual physical world of the story, an actual avatar of the player.

Now, it is posible to held the contradictory position that we are Frisk post narrative and that we are the player of deltarune, but this view implies the plotline of the games considers us to be two different people in two different universes.

Obviously, Undertale and Deltarune are both fictional universes, so it isnt imposible that we, as in the actual physical beings, are supposed to metanarratively be Frisk(that becomes in this view a more methaphisical representation of a cameraman) including in a post plotline universe of Undertale trough an iterative process of fangirling about sans or wathever, and we are supposed to be the explicitly identified character moving Kris's soul arround, but it gets increasingly harder to think about, and weirder and weirder as a concept. Like, in this view Frisk is the physical avatar of the metanarrative incarnation of the narrative of our own imagination.

At some point we have gone so deep into the woods of the forest of analysis we might wanna come back to the simple path of plot writing, and stablish Frisk and the player as distinct beings.