I feel like OB starts with an target aesthetic, and works backwards from there. I mean that in the fondest way possible because what truly snagged me and hooked me on this show above others is just the sheer beauty of all the fanart, and I think that's tied to OB being a visually beautiful show.
So like the strongest part of OB, for me, is that it constructs these really intricate and awesome sets, and then sets Tatiana et al loose on them. So you've got an awesome environment and really present characters, whose motivations are always really clear (in regard to some tangible goal, not just love interests / emotional arcs- I want the briefcase; I want to start a new life with Kira and Felix; I want to maintain the order of my perfect life... I want to find out if 324B21 is self-aware, etc.).
But, at least for me, I feel like sometimes the emotions of individual characters kind of get dragged under and swept along by the setting and plotline. I suppose this happens in life also, and it's kind of a swinging door: like when a character approaches a fork in the path, and I see them choose one of two roads, but am not entirely sure as to why, I'll sometimes rewatch and clue into the "emotion" / tone of the show by focusing on the setting and how things are lit etc., and then extrapolate from there about the emotional state of the character(s). I guess what I'm saying is that OB seems to use visual clues to fill us in on the emotional states of its characters.
So to get back to my point, I feel like the off-screen reset was necessary for Cophine to get to the emotional point they needed to be at to fit the visual "tone" that the authors had in mind for the Dyad scenes this season.
So to facilitate some target scenes / huge visual set-ups, like having Delphine and Cosima cut open a clone of Cosima, which is playing with both body-horror and the idea of paranoia/betrayal in a relationship... you need something sitting on the other end of that teeter-totter, to balance out that darkness, kind of?
Say the target tone is "ominous" (at least that's what I'm getting from Dyad sets). Ominous, implying that something is coming- a fall is coming for Cosima. But for a fall to matter, it has to be from a high place. Delphine needs to be Cosima's high place to fall from, because her life pretty much sucks right now.
Like amidst the starkness and creepyness in the Dyad sets, you have the warmth of Cosima's stuff (and Cosima herself, always dressing in red).
And Cosima's outlook in general is pretty bleak right now, so I think they needed Delphine to be that blot of red for her, emotionally, right from the beginning, or Cosima's story would feel unbalanced. ...?
I don't know if any of that made sense as words.
Also, the environment is impressive, but totally menacing. So Delphine needs to feel like a true threat to Cosima for the tone of the storyline to match the visual cues of the setting, since Cosima is spending most of her on-screen time with Delphine. And I think the only way you can play with paranoia the way OB likes to, is if there's some trust there for Delphine to betray.
...At which point you're probably like, duh, that's my point- why couldn't we see her gain that trust? And I'm like I don't know man, but I wanted to talk about colors.
I've totally lost control of this post so I'm going to stop now.