This third angle was most unnecessary. Because the makers CANNOT show Dev wavering from his marriage. So what is the point of this track? What is the whole point of bringing her in, when everyone knows that it won't be reciprocated? Regressive or not is a topic of next level, if Dev had been shown to be inclined towards this woman.
This is the most pointless, useless track.
It would have made sense if this was Sanjana's story, if she was the protagonist, that she loved someone, but it wasn't reciprocated. Like DTPH was the story of all three, Rahul,, Pooja and Nisha. But Kuch Rang is not Sanjana's story in any way at all.
This is Devakshi's story, their relationship, their families, their lives. So this Sanjana track, of one-sided love adds no value to this journey they are taking the audience on.
As for showing women as homebreakers, I agree that is regressive.