slower relationships that do exist (none could reach sex before the end of act 3 to give time for the relationship to develop)
I feel this his highly restrictive to story telling. The two romances I have experienced are Astarion's and Gale's and I like them both the way they are. For Astarion's story it is important that it starts physically and develops into a sincere relationship - at least in his Spawn ending. The Act1 sex scene you get with him is staged as a scene from a cheesy romance novel, the dialogue, the lighting, the way he presents himself to the PC. It is so delightfully over the top fake. I love it. It perfectly gets the point across that this is a performance. By contrast the romance scene on the graveyard is much sweeter and much more sincere. In Gale's case the funky Astral Tantra in Act2 looks odd, but I do love what it represents, a joining of souls. The whole illusionary forrest scene is about giving this seriously depressed guy a connection with another person both in the friendly and the romanced version, so it makes most sense to have his big romance scene here. In his case the physical sex scene with the bed fades to black quickly, while the more elaborate one is more representative of a deep emotional connection and has the dialogue to accompany this.
Saying no sex before Act 3, until you know each other very well, is leaning very heavily into a conservative "no sex before marriage" thought pattern and only allows for very normal relationships to happen.
That said, I could do without Halsin, the Drow and I guess without Minthara - but I don't know "the woman who wears Astarion's armour" well.
The thing with the emperor though, I actually like, because it is one more step on his grand plan of manipulation. It's deliciously vile and creepy.
