Yep, that's pretty much what it amounts to. He abandons everything that had been so important to him because he can't accept Loghain as a fellow warden.
Agreed. If you encounter Alistair as a drunk in the Hanged Man in Kirkwall, one of the things he says is, "I'm sorry Duncan, I failed you." I suspect, based on some of his other rantings, that what the writers intended for him to mean by that is that because Loghain didn't get executed at the Landsmeet, Duncan went unavenged. I think the truth is more that he failed Duncan by deserting the Grey Wardens during a Blight.
To a Cousland who, as their father lies dying on the floor of the larder, says they want revenge against Howe, Duncan says, "A Grey Warden's duties take precedence, even over vengeance." Apparently, Alistair never got that speech.
Don't get me wrong, I LOVE Alistair. If he doesn't have a gigantic tantrum and abandon his duties because you decide to take the advice of the Senior Grey Warden and recruit Loghain, Alistair is great. He eventually makes an okay king if he's hardened, and he makes an excellent Grey Warden. But the "I'm deserting my duty because I can't have my way" thing really IS a slap in the face, and seems, at first, out of character. But then think back on the story he tells of his mother's locket and how he had a big tantrum and smashed it. Some things really never change.
Given some of the bits and facts we know about abandoned story turns, I suspect he was only supposed to have that tantrum if he was unhardened, and that he would have otherwise stayed (given the existence of conversation snippets where he and Loghain are talking to each other and the fact that at one time Loghain could be recruited much earlier in the game). That makes sense from a character perspective, but then they wanted to force the whole Dark Ritual thing so they created the "bottleneck choice" and broke a lot of things in the narrative (IMHO) in doing so.
Anyway, I do think Alistair's sudden hatred of the Grey Wardens because he couldn't execute Loghain is ham-handed story development, as it stands in the final version of the game. It is DEFINITELY Alistair deserting and betraying the Grey Wardens, and failing Duncan in the process. And, if you were romancing him at the time, breaking your heart in the most humiliating way possible (I have never spared Loghain when romancing Alistair, I just couldn't; I did create a game file to import into DA2 so I could see what Alistair the Drunk was like, though. And the one time I did spare Loghain, I arranged for him to marry Anora first, so I knew he'd be all right. Told you, I love Alistair.)