"PS: 3 out of 4 comes from DA2 compared to 3 out of 4 from DAO (most popular), proving once again, DA2 is the most unpopular game in the franchise. Also, I have left out Loghain and Tallis, my bad."
I do not think the two correlate to each other. Carver is a companion who, if you play as 2 out of the 3 classes available, is only a companion for the first 10 minutes. And if you play as a mage, he's only available for about half the game.
Sebastian is a day-one DLC companion - which made a lot of people hate him from the start, just on principle. But if you don't have the DLC, you never have him, and if you do, you only get him for half the game - during which he has less content than the other companions.
I think all the DA games have good and bad companions. Overall, for instance, I like the ones from Awakenings the least. But since they're only around for such a short time, they aren't as offensive to me as the ones I dislike from the other games. I don't think it's fair to say that a game with some companions I love and some that I hate is worse than a game where I feel "meh" about all the companions - but when voting for the worst companions, of course the ones I hate are going to beat out the ones I'm "meh" about.