I suspect that what people asking for longer development mean is that they want more development before the first night. I wonder if that comes from pattern of games typically saving the first night and the official forming of the relationship for the end of the game? Once you get that and maybe a couple interactions after, then the romance part of the interactions tend to end, beyond maybe one or two repeatable lines or comments. So maybe that request is just due to people feeling instinctively like the party scenes are the end of the romance, because that's how other games of this sort have trained their expectations? If you think about it, it's actually not just games. In most media involving romance, the actual formation of the couple is saved for the end as a climactic moment. When was the last movie you watched where the main romantic characters were truly together before the end of the movie? Usually if the characters were together, they're estranged or the relationship is on the rocks, it's somehow fractured. The romantic plot is about them repairing the fracture to come together again by the end. And look how often in serial TV is the romantic tension the will-they, won't they? And when they actually do get together, if the show keeps going significantly past that point, usually the relationship breaks up and they redo the plot or replace the love interest with a new one entirely. It's rare for media, especially popular media to follow a stable relationship significantly through its run. Add to that the fact that after the first night, we don't get many romantic nods beyond one conversation, it seems. So again, people's narrative instincts are making them see the first night at the party as the end of the meaningful romance portion of things.
Having said all that, I actually don't think the romantic development we've seen is that bad. I've only seen Gale and Shadowheart's so far, but I think it makes sense for Lae'zel to be reticent and not really show romantic interest until the end. Same with Astarion, though I haven't actually had him in my party very much so I'm sure I've just not seen any scenes that might set up his romance. Wyll, I have him in my party a lot and he also doesn't have much setup that I've seen. But looking specifically at Gale and Shadowheart, I think they're both very well done romances so far. Gale's romance effectively starts at the Weave scene. I found it a really good moment. It was so good that I, someone who basically never romances guys in games, actually decided to do romance him then and there. From there you get a handful of other romantic interactions throughout the act that I think are very cute and effective. I think that the sex scene at the party is earned by that point and really feels like the culmination of a budding romance. The way it reads to me, if you forgive him for dropping the Mystra stuff the morning after, you're a full on couple from there on out. That's very interesting to me and I look forward to seeing that play out in the full release. I really suspect that however consciously, Gale is manipulating us for our help and the conflict of our relationship is how much is he able to truly care for us compared to his longing for Mystra.
Shadowheart meanwhile, she also doesn't get many scenes that really imply romance, just the opportunity to flirt here and there. Her party scene is a traditional beginning to a romance. And a really good one too. It's the classic 'moment you both let your guard down' scene, where camaraderie turns into something more. Structurally, it's her equivalent to Gale's Weave scene, the moment when the romance truly starts. It's also not a sex scene. The way you refer to it in the conversation after makes it really seem as though you both just kissed and that's it.
I suspect that the fact everything for everyone comes to a head at the party. It was absolutely worse in early patches though. I just went through the party scene and those interactions do feel more natural overall.