On my very first playthrough of DoS2 I ended up killing Sebille and leaving her behind. I didn't get to learn her story and my opinion of her character pretty much mirrored how most people seem to view Astarion. It was only on subsequent playthroughs that I took her with and learned the rest of it.
And. My opinion of her didn't really change that much, but it did change some, I'll admit. Maybe I just found other characters more sympathetic. It's interesting how people judge the whole character based on the first act of the game, Sebille and Astarion both, and how people seem eager to take Astarion, a known liar, at his word. I don't expect a full heel turn in his future, but I do expect a version of Sebille's kill the slave master storyline, just with the names and actors swapped out.
But the community reaction to both Sebille and Astarion is absolutely the same, at least judging by conversations based on this forum and reddit. They are both the most killed and the most disliked of the companions so far. The only difference seems to be that occasionally Astarion is funny, which means people kill him slightly less.
That's about the opposite of how I imagined it being, given how everywhere else everyone seems to be practically worshipping Astarion and hating on Lae'zel (who doesn't really deserve it, honestly, because in her case her personality and attitude are completely in character for her race, and having the polar opposite of the githzerai companions that were in some of the older games is both interesting and refreshing). I am surprised to hear about the hatred for Sebille as well, honestly. You'd think more people would despise the Red Prince instead, who's actually closer to Astarion in character at least on the surface (outward attitude) level, but nope. Or Beast, who's probably the least developed of the cast (the fact that his background seems to have changed at least once during development - he used to be a, well, beastial and savage dwarven gladiator - must have played a role there).
Staying away from any forums and communities back when D:OS2 released to avoid spoilers sure had an effect. As for Astarion, I am pretty sure his storyline isn't gonna go towards liberation and redemption, but rather to taking the reins and claiming the power for himself, if his character is any indication. Just a guess.