I honestly don't see Astarion and Halsin as star companions too. I would like an explanation too, if that's ok.
I meant it in the sense of they were the stars of the companions - featured most in publicity and fan worship rather than in game, story-wise. Pre-release Astarion was probably the most talked about companion yet now he is hardly mentioned. Halsin was talked about less (will he be the missing origin character and all that) but now he only features on the forum because his Act 1 and Act 2 quests bork.
Ah, ok, I understand, what you mean. I do agree about Astarion, I mean, he was made to draw in the not so typical DnD crowd, so he was featured widely. I don't really agree about Halsin - apart from the bear memes everywhere, I don't see him often featured outside of talks in this or other BG3 related forums/reddits. And I'm pretty sure, most people remember 'the game has bear sex', but not, who the bear is. You often have to explain, that the 'bear' is actually an elven man.
Before the whole bear thing, he had the "Daddy Halsin" moniker going around.