I try and assume nothing since my days in the military; still get hoisted from time to time, though. But in this case, we know the Tower is closed for at least a full day while we explore the Wilds, and night has fallen by the time we return to it.
And they did have an Ogre; we had elevated terrain, fire, oil, etc. The Darkspawn were underestimated; another feather for those in leadership roles. Etc.
It again comes down to responsibility, and how it is managed in the future. Loghain continues to allow things to become worse. This says little to me about regret, repentance, restitution, or even asking for mercy. It says more about hate filled pride.
Uh huh. Right. I can't speak for military experience, but I'm not seeing why Loghain has to have all the blame beyond willing it onto him. No one expected the darkspawn to attack. The in-game dialogue says they found some lower chambers and the tower was sealed off while they explored and secured them.
For all we know, the lack of preparation, or vigilance on the part of Loghain's men in the tower may have had nothing to do with him and everything to do with the soldiers themselves not expecting any action and thus were caught with the trousers down, so to speak.
And the soldiers not expecting an attack, no messenger sent to Loghain to inform him the tower fell, and everyone expecting the tower to be a boring post with no action may have also had the soldiers and the whole thing with losing the tower and the tunneling, which is a tried and true medieval tactic to weaken the structural integrity of fortresses, may simply be a few soldiers got lazy and screwed the pooch for everyone else.
Add in that the Chantry would not let magic be used instead of the tower, Cailan's insistence for a war the bards would sing of for centuries, the wardens secrets, and only seven mages (unless the warden is a mage himself, then eight) were actually at Ostagar, not all of Ferelden's forces were mobilized, they were outnumbered considerably but no one in the camp actually knew the size/strength of the darkspawn because the scouts reports didn't have a complete picture, and it's pretty clear that no one, maybe not even Duncan, knew the full strength of the horde and so everyone underestimated him.
Walking around Ostagar, you'll hear soldiers wondering where in the world the darkspawn came from. It's in the lore that after the fourth blight, the entire surface just decided that darkspawn were extinct because so many were killed in that final battle. And in pretty much every origin, save the dwarf ones, no one is taking the darkspawn seriously because no one, save the wardens, think it's an actual blight.
I don't see any hate-filled pride. Sure, Loghain is a proud man and thinks he's the only one who can protect Ferelden, but when you take into account that Ferelden nobles start wars with each other over trees, it's kind of hard not to think that way. So he is proud, paranoid, hates Orlesians, but that doesn't translate into plotting to kill Cailan and usurp his throne.