To the original post I never did like Loghain but that may have been since my first play through was as a Cousland and he seemed very friendly with Howe more then anything he did at Ostagar. Of Couse as the game went on and more and more of what he was doing was revealed he earned my dislike along with Howe. He may have been innocent once but their was a time when Hitler, Stalin, Mao, Calligula, Attila, and every other mad man who committed atrocities was innocent or respected. Hell, Hitler was noted for heroism as a soldier in WW 1 and if he had died then no one would have a bad thing to say about him, but people change.
As for the battle itself you have to remember several things.
1. Loghain has no track recorded as a successful battlefield commander. He rose to fame and glory along with Maric who was an able commander in his own right and together they led the rebellion to several major victories and crushing defeats. Sure they were facing a larger and better trained and equipped force but that is the point, they avoided battles in the field because they had little chance of winning and so fought a guerilla campaign. In fact Loghains ultimate victory at the Battle of River Dane was not some glorious victory in the field that proved the martial prowess of the Ferelden army, but an ambush of an army on the march not equipped or prepared for battle as they were crossing a river, likely with a long drawn out wagon train that had to be protected making it almost impossible for the Chevaliers to respond quickly enough to drive off the rebels. I would be surprised if even half of the Orlesians had been in armor considering they are described as a heavy army most of the Chevaliers would likely have put there plate on a wagon rather then wear it during a day of long marching or riding beneath the sun. And his victories over the other Banns during the Civil War were more then likely simply a matter of numbers and supplies. We see that Loghains army at Ostigar is massive and fully equipped with heavy chain and with his power as regent he set about rebuilding the royal army adding it to his own. The Banns may have been able to gather enough men if they were united but they are prone to infighting and petty grudges that divided them and have to equip them with their own coin from a few farm holds. I'm not saying Loghain isn't cunning or efficient, but I do feel he is given more credit then he deserves as a general.
2. Callen offers to postpone the battle and wait for reinforcements from Orlais but Loghain forcefully states they don't need any help. I know he doesn't like Orlais but if the combined might of the Royal Army, the Teyrnirs of Highever and Gwaren, along with several Banns isn't enough to stop the darkspawn then they are going to need help or all of Ferelden will be left at the Darkspwarn's mercy. I don't think he's that blind at this point in the story so he must honestly think they have enough men to defeat the hoard. If nothing else the heavy Orlasians could have been used as cannon fodder holding the line while the entire Ferlden army launched the flank attacks.
3. The most important is the fact that he doesn't think this is a blight. Darkspawn are animalistic creatures. The shock of thousands of heavy infantry crashing into their flank while the royal army was still fighting in there front would likely have caused confusion and panic if this was just a very large band as he believes. Without the presence of the Archdeamon in the mind crushing their will and driving them forward they are shown to panic when faced by dedicated defenses without a vast numerical superiority which, while Duncan says they look to now outnumber the army it doesn't seem to be by a large margin. Most of the ground they took in the Deep Roads was during the first blight before they turned to the surface since then they have been in a slow war of attrition with Dwarfs which they could have won centuries ago if they had been determined to overwhelm there defenses, but they aren't. The battle of Dennerim is my chief example in cannon but even outside that bands of darkspawn roaming the boarder and attacking towns between blights are considered a nuisance not a real threat by most people.
4. As for survivor accounts they needed to be taken with a grain of salt. Any one from the Royal Army watched as their line crumpled and they were completely overrun by darkspawn. They only survived by running away while their comrades fought on and died buying them time to get away. I'd wager most suffer extreme guilt and some form of PTSD from running away while the rest of the army fought to the death as was honorable. As for Loghain's soldiers while I believe they believe there was nothing they could do most had no idea what was happing. They were hiding to the side of the battle so they could charge into the flank unnoticed and they needed the beacon to tell them when to charge because they could not see the battle and so could not tell when the time was right. The fact that he calls for retreat the moment he see the call for help without even scouting the field tells me he had not intention to help. Maybe he thought to long had gone by or maybe he planned it either way I'm sure he told the men he pulled them out of Grey Wardden trap and saved their lives when they began to question how the Royal Army had been wiped out when they hadn't even been committed to the battle and as a respected war hero they believed him.
So yes, I do believe he quit the field and abandoned the king and his army to death. I'm not saying charging would have won the battle, it may have done little more then get himself and all his men killed to take down some more darkspawn. But even that would have meant that the Warden would have had an easier time gathering the remaining forces of Ferelden while the Hoard was delayed in gathering its strength since it would have lost thousands if not tens of thousands of more darkspawn in his charge since human soldiers are shown to be worth several genlocks or even hurlocks.
And just to make this longer I do have to say I don't think he poised Emon before the battle. Duncan brings a message from the Arl when they arrive so he had recent contact add to the fact that a mage warden was recruited the same day as Jowan fled while Loghain was with the King in the south and he is said to put Issolde in contact with Jowan means that he simple couldn't have done it before hand. Right afterwards as he was marching back to Dennerim? Maybe, but not before.
Really he may have just been in over his head with to much placed on his shoulders. Honestly the way we see him unravel as the story goes on I think this may have been what happened. He has been praised as the hero of Ferelden for decades and now it's facing the greatest threat since the occupation and only he can save them from it, even Duncan says so, but he just isn't up to the task and the harder he tries the worse it gets. Don't get me wrong, I spared him only once to see that content because I'm a completionist, besides that I always do the honors myself.