Oddly enough though Astarion's romance IS certainly the most romantic, but I also feel he's just skilled in that regard, which keeps open the opportunity for betrayal if things go south. Luring people and keeping them charmed was his job.
Absolutely. Every time I click on him and he feeds my character one of those sugar-sweet romanced lines, he gets a mental side-eye from me.
But I keep romancing and clicking. Because he really is good at his job.
True. And -- as you say -- it is because he has been written as a seducer but it is also due, in part, to the fact that he has the greatest potential for growth as character. In the morning after scene we (literally and figuratively) see how wounded he his and how his life would improve were he freed of his master.
Shadowheart had the same potential but Patch 3 kinda ruined her. She went from being a tough nut to crack, the person who lets very few people past her armor, to someone who gets gushy and cuddly after a night of kissing.
Notice how Shadowheart's meme economy has fallen while Astarian's has risen? Before the SH changes people were making goth-shadowheart / shadowheart disapproves memes. Now that she's gotten so darn agreeable people have turned their attention to the traumatized vampire spawn.