I also wish there was a little more ace/demi-friendly romance around, though I'm not sure how easy it would be to add in (I agree that it seems easier for some companions than others).
Imo, I think part of the problem is that the pace of the relationship seems entirely dependent on the COMPANION, not the player. For example, if you're romancing Astarion, you have to sleep with him early on. There's no option to tell him that you'd like to wait, or that you're interested in a non-sexual relationship with him. I haven't experimented with the other romance options much, but from what OP said, I'm assuming they put you in a similar situation. I wish there was an option for all of the characters to wait until the end of their arc ("wait until we know each other better"), because even someone interested in a sexual relationship may not want it right off the bat. And while yeah, companion characters may have their own preferences... this is still a game, and they were all designed to be attracted to the player regardless of race/gender, so I don't see why some flexibility about the pace of the relationship would break with the design philosophy. At least having the companions who will eventually "require" sex slow things down a little so you can get to know them before making that choice.
For Astarion, he could still try to "seduce" the player character while keeping their actual desires in mind, since his goal is self-preservation. (I personally think it'd be kinda funny to watch him try to figure out what to do to "seduce" someone without actually sleeping with them, but that's just me).
For Karlach, I could maybe see an option to have some level of physical affection, like hugging and cuddling, without having to require sex asap.
For Lae'zel, I ran away from her flirting too fast to pay much attention to how her attitude might play out with this.
For Gale, Wyll, and Shadowheart, I feel like their romance storylines wouldn't be too hard to adjust for a character who wanted to delay / exclude sex.
Obviously, this would make things a lot more complicated to write, so I don't really blame the writers for not investing their time here.
Honestly, I think my main wish was just to have dialogue options that better express my actual thoughts. There's no way to distinguish between "I'm in into YOU, personally" and "I do not sleep with people that easily" / "I don't sleep with people, period." The game seems written to expect that everyone has a high sex drive by default most of the time, and while that's probably a good match for a lot of people picking up the game ready to date their companion of choice, it got frustrating at times to not have dialogue options that reflect what's actually on my mind. There were definitely a few times where I wished for something more like "I'm into you as a person, but I don't like jumping into physical relationships that quickly." Kind of like that one scene of Gale's where you could choose between imagining a kiss or imagining holding hands -- I really liked that option for expressing an interest in romance that wasn't so focused on sexual attraction.
Somewhat related, but I think there were one or two places where I also wanted the option to say "I have an EXCLUSIVE partner already" I think with some of the side characters; it felt very strange to be responding to these as if the sole determining factor was how I felt about the character propositioning me, when my point would be more like "It actually doesn't matter whether I'd be into you or not. I'm already committed to someone." (These would be minor tweaks and it was really weird to me that the option wasn't there, since the origin companions are all exclusive to each other)
I certainly feel like there are bigger priorities of things to fix with the writing if they're going to be making changes (Hello, Act 3...), but the game does seem to pride itself on the companion interactions, so having some more flexibility with the relationships would be nice.
