did he really needed to make scapegoats from us btw?
from his perspective, we were in fact responsible for Cailan's demise.
Look at it this way:
Historically the Wardens pledged themselves to help spread the Chant of Light at Drakon's behest, and he was the one who formally created the Chantry today. It was one of many cults at the time but his favored one dominated the land through his Exalted Marches of other city-states in what is now Orlais. The Chantry and Orlais are deeply intertwined, so they have had a history of being Orlesian agents.
Two hundred years ago, the Wardens were exiled from Ferelden for conspiring to overthrow the crown and place one of their own on it. The truth about the rebellion, and that Arland was a tyrant, wasn't known in the modern era as most of the records of that time were destroyed in the civil war that followed Arland's death. All that was known was that the Wardens were about to cause a civil war to kill the king of Ferelden at the time and they were cast out of Ferelden for it.
Already a poor track record.
Then fast forward to twenty years ago where Loghain saw some of the Wardens collaborating not just with an Orlesian First Enchanter bent on giving the King of Ferelden over to the Emperor, but also work towards corrupting all of humanity with the Darkspawn taint.
Also bad for their image.
Then, look at Ostagar itself. The Wardens kept their secrets from even the head of state and his general, when such things should be told to them so that they at least understand the Wardens' necessity (this is made even more glaringly stupid when you factor in how in the Calling, Duncan and Fiona and the rest blabbed their secrets to Maric. So why they don't do it now is beyond me).
So they tell Loghain nothing other then "We feel it with every fibre of our being that this is a Blight" which just sounds like guesswork to most people.
Throw in Cailan's idiotic gloryhounding persona where he thinks just being near the Wardens is enough to turn the tide of the battle, strategy and consequence be damned. The Wardens did nothing to reign in his mindset and tell him that while they are powerful and needed in the Blights, they cannot pull a victory out of their asses just by being there.
Then look at Ishal. The tower is taken by the Darkspawn, but Loghain doesn't know this. What he knows is that Alistair and the Warden should be at the top of the tower and light the signal when the forces in the valley send theirs up. We had less then one hour to get to the top of the tower and watch the battle. When we do light the beacon, we're late (as Alistair says) but also striking it at the wrong time as the plan called for the beacon to be lit when ALL the Darkspawn were committed to the battle, which they were not as you can see the extent of the horde goes to the ass-end of the Wilds and they were still coming into the valley when we light it.
So what Loghain sees is an order with a checkered history lighting the beacon at the wrong time when Cailan's forces are cracking under pressure, in the hopes that Loghain will be a romantic fool and charge in to save the king, thereby dying in the process. Ferelden would lose its king, its best general, and a large quantity of its troops.
Then, with a power vacuum in place, a civil war would erupt for the throne and weaken Ferelden further, and Orlais would swoop in to "save the day" as they had done to Nevarra and Kirkwall in the past (the former during a Blight, the latter during the Qunari Wars). Problem being, every time they save some place they never leave and have to be booted out.
So in Loghain's mind, the Wardens were indeed one of the biggest reasons Ostagar was a flop. In his mind, they were never going to help Ferelden stay independent and safe.
Is it paranoid? Sure, but it's also grounded in historical fact.
As for Eamon, I also forgot to mention that Howe also shares blame in that. He didn't give the order, but he did have a controlling hand in the situation (Berwick answered to a man in Howe's employ, and Howe is a power-hungry weasel who would stop at nothing to get more power and lands in his hands.)