The thing is, Gaider's word isn't completely without evidence in-game to support it. We have the huge darkspawn column visible from the bridge, which goes all the way out to the horizon. That, I think, supports the "completely unwinnable battle" idea. We have one of Loghain's soldiers angrily argue against Leiliana's both Leiliana's spoken assertion that he's an unthinking lapdog and the unspoken assumption that everyone not on his side holds that Loghain deliberately betrayed the king, which if it isn't evidence of the truth of the matter he asserts at least leads one to suspect that it's not entirely clear that Loghain is lying. (Don't get me wrong, you'd expect to see one of Loghain's soldiers supporting him either way, and especially in public after circumstances lead to every single person listening to his words; most of the reason I think he works as a witness is because of the vehemence of his belief. He doesn't stutter, he doesn't look abashed, he doesn't show any sign of doubt that Loghain saved his life.) We have the cutscene in which Cailan dies, which shows darkspawn still entering the valley shortly before Cailan is killed; Loghain's strategy becomes much more effective the more darkspawn are distracted fighting Cailan. (This last one by itself doesn't necessarily preclude victory, but taken in context with the unending column visible from the bridge it looks pretty bad.) And during the DLCs we have a dying member of Cailan's honor guard casually accepting Loghain's presence in front of him (should the two meet), and casually agreeing with Loghain's assertion that the battle was already lost. The weight of these bits of evidence varies, but at the first one should qualify as clear evidence of the necessity of Loghain's retreat, if not of his motivations for doing so. And should we accept that it was necessary, why do his motives still matter?
I'm going to play the Devil's Advocate here. That which you call a darkspawn column I call an unidentified column of lights. Considering the fact that none of the darkspawn we saw were carrying torches (or any light source for that matter). What it is, is unknown. What it suggests is of course debatable. In regards to that soldier arguing with Leliana you make the point quite clearly that he wouldn't exactly be privy to Loghain's thinking or his plan behind the plan, so his reaction is understandable, albeit misguided. Just like the guy you fight (or not) in Denerim. Still, what he says doesn't constitute proof without knowledge of what Loghain was thinking. Vehemence doesn't imply fact. By the same token, Alistair could vehemently proclaim that Loghain betrayed the king, which by your measure would hold equal weight. As to the darkspawn still entering the valley before Cailan is killed, well, Cailan might have been killed either way, but without the benefit if seeing how the planned counter from the flanks would work, we'll never know. Plus, I doubt that in the midst of battle, one man's death (even a king) will cause much of a wave when the enemy is still bearing down on you. If anything it might inspire more of what you saw from Duncan... And on that note, consider the notion that the scene was almost certainly intended to reflect the magnitude of the event. Of course people are free to interpret it however they wish.
In regards to the DLC you mention (I'm thinking Return to Ostagar), I don't know how much weight I'd put into an NPC's non-reaction to something that is obvious to us. BioWare's games are rife with that and notorious for "sins of omission", so I wouldn't exactly call that proof. Likewise, his comments (to me) are just fodder to justify the existence of the DLC and really make no sense. I say this because there's nothing to suggest that what he says is a reflection of Cailan's thoughts. To that, I reference Cailan's brief exchange with Duncan. From that you could conclude that he believed Loghain's plan would work and there's nothing to suggest otherwise. The look on his face and the conviction with which he spoke said it all.
{I'm going to play the Devil's Advocate in regards to my own assertion here. I'm slightly inclined to think that it was the intent of the writer's to portray Cailan as somewhat of a visionary. His decision to send Alistair and the Warden to light the beacon seemed oddly prophetic, considering the outcome. This would in essence lend weight to what you reference in the DLC and would then make your assertion plausible. That being said and with nothing to justify or clarify that point, I continue... 
}
So, I respect your opinion, but mine remains unchanged. Not because I need to be right (Believe me, I don't. I'm all about facts.), but simply because the evidence (in my eyes) doesn't support anything beyond Loghain's hubris and treachery, which I say is the intent of game and the impetus behind your character being who he/she is regardless of what their decision is at the Landsmeet or what you the player sees as justified or not. I'd even take it a step further and reference comments made by Aveline and Varric in DA2, but that would be going beyond the bounds of this thread.
Ultimately, as I said in my earlier comment, even if I wanted to believe that Loghain's actions at Ostagar were militarily sound, everything he did in the aftermath sealed his fate. I could dismiss Ostagar entirely and still arrive at the same conclusion. In that sense, I'm only answering the question that was asked in the beginning of this thread.
Retour en haut
*laughs* You definitely went the "questionable" route (as my Warden would see it), but hey, they're all viable options, so... *shrugs* Without going into detail, I'd say my guy was a "pragmatic good" type who felt that the events at Ostagar (including the return) and all that followed, removed the veil of innocence he wore, having lived his life in the Circle. From that point on, he took no *guff* from anyone. He strove to do the right thing, as he didn't want to give people more reasons to distrust mages even though he did become a blood mage. (The option was opened in Awakening, not during Origins. 
