It's possible that they have changed it and made it overall easier to choose the good route, because on my current DU run, my DU told her to do whatever she wants, and even with just 'fair' approval she didn't kill Aylin.
It's wild that the game wants you to blindly trust a companion with whom you have a "fair" relationship to not kill an important NPC, despite her clearly expressing the will to do so a few seconds ago.
I agree about the fact that it's barely mentioned in the main storyline (I only remember Withers' line about it and nothing else), it would be a good thing to elaborate on. But the companion plot is affected by the romance with him, there are special lines, and the companion plot and choices affect the romance with him.
I can't comment on the Astarion romance, but I've seen people here complain about the "painful sunlight" ending for him, where the PC boyfriend just stands there having a great time like the rest of the team. My point is that romances should matter a LOT even through the main storyline, not just in isolated cutscenes. At least there should be no incongruence between these two realms of interaction.
Though I will also say that Larian oversold just how complex the romances in the game really were.
That's where my "dating simulator" hyperbole was aiming at. The amount of "playersexual" interactions feels weird and intrusive. Even if you go for the experience, the payoff is underwhelming. This "dating sim approach" also influences the selection of possible companions we get. They are all young, conventionally attractive looking and super horny. No ugly half-orc, or smelly old dwarf. No shorty companions whatsoever because well all know that shorties are not sexy...
