Agreed. I get why Alistair liked it so much; it was a welcome change-of-pace from living in the monastery where he had no friends, but calling it "an honor" for everybody else is stupid. It sucks for anyone with a comfortable and happy enough life, and the Wardens are notorious for accepting any old scum that can fight and survive the Joining. At least Loghain was once a war-hero and liberator before "going bad."
I also found his heartbreak over Duncan to be a bit eyebrow-raising, comparing it to someone losing their parent when Morrigan calls him on it. WTF?
Then again, the same way that becoming a Warden can suck for someone living a cushy life, losing Duncan can seem like no big deal to someone who has had any sort of loving family to speak of growing up.
Alistair had no one growing up. Never knew his mother, his biological father didn't acknowledge him, the closest thing he had to a father figure growing up had him sleep in the stables and kennels like an animal. Then said foster father didn't stand up for Alistair when his new wife started going out of her way to make his life miserable, then he just sent him away to a monastery when said wife demanded it. Then the instructors at the monastery were severe with him and the other students ostracized him for his blood.
Alistair didn't know what it's like to be loved, needed, or part of a family because, while he was growing up, everyone treated him like an inconvenience at best, an unwanted burden to pass off to someone else at worst. Duncan and the Grey Wardens were the first (sadly enough) to like him, welcome him, and accept him as one of their own.
BESIDES, Alistair doesn't necessarily equate losing Duncan as losing one's whole family. You're taking that out of context. When Morrigan "calls him out on" not getting over it right away, he says, and I quote: "Is my being so upset so hard to understand? Have you never lost someone important to you? Just what would you do if your mother died?" He's not saying that losing them is the same as losing one's whole family, he's saying that they were important to him and that's why he's upset. He then appeals to Morrigan's sense of love and attachment, but probably knows she hasn't gotten close to that many people as a reclusive "witch of the wilds." Since her mother is the only person he knows she spends time with, he asks what about her? It backfires since Morrigan says "Before or after I stopped laughing?" but the sentiment is there.
If you found it "eyebrow-raising," then you and your character have been highly privileged indeed.