I can totally see that. First playthroughs really affect how you ultimately view a character, since that was your first impression of them. I love a first playthrough, especially unspoiled. You're just bumbling about and have no meta knowledge, and things are so fresh and real. I think that's why it really makes an impression.
I just happened to fall into a good Alistair on my first playthrough. I started out as a Cousland, seeking revenge for my family. I cared about the darkspawn, because I cared about Ferelden and I played a person with strong country ties. Since Howe & Loghain were working together, there was no way she would spare either of them. She had enough persuasion at the beginning to talk to Loghain in camp, in Ostagar. So after that conversation, when he knowingly left her there and took in Howe, knowing what he'd done to her family... no. Plus, she wanted a strong Ferelden, and to do that she didn't want any divisiveness among the nobility. I accidentally hardened Alistair that first game too (didn't know it was a thing), so he was ready to take the throne, and rule together. (edit: I did however, write a story based on drunk Alistair, that is still one of my favorites, though I never completely finished it. The storyline of him leaving does have great potential... but only if I can be in charge of guiding it! lol)
In subsequent playthroughs things were different, of course. Especially in my dwarven & city elf games!
DAO was the first video game I'd ever played that had cutscene romances like this, and Alistair the first video game character I ever fell for, at a time when I was getting out of an 8 yr relationship... so I'm sure that colored my view, too!