Thank you, OP, for this thread. I've always found Riordan to be the shifty sort of character...
Okay, first off, when you meet him in the dungeons, my Warden always, ALWAYS asks about reinforcements. Because we've heard neither hide nor hair from the Wardens at large, who are apparently content to let two very junior Wardens wander around Ferelden without a clue. Riordan tells us about Loghain closing the border, the Wardens implicitly wanting to make Ferelden an example of by being destroyed by the Blight, essentially consigning not only hundreds of thousands of people to death but of those, thousands of women, old, young, children, to be raped by the darkspawn into Broodmothers.
Yeah... the Wardens are a nice lot, aren't they? We get confirmation of this throwing of Ferelden to the Archdemon in Warden-Constable Blackwall's letter., seen in the World of Thedas, Vol 1. So Ferelden is to be Thedas' sacrifical lamb, just because Loghain refuses to let the Orlesian Wardens, with four legions of chevaliers in. Clear enough.
What, then, is stopping the other neighbours of Ferelden from coming in to help? The Free Marches are directly north of Ferelden. Kirkwall is closer to Highever than Highever is to Denerim! Where are the Marcher Wardens? Not a single one? Really? It's difficult to imagine Loghain having any objections to a Marcher contigent of Wardens - especially if they didn't insist on crossing the borders with the same army that raped and pillaged Ferelden for a century. Apparently, the First Warden REALLY wants Ferelden to be made an example of - and Riordan is curiously unconcerned with it. Despite claiming to be "born in Highever," his accent and mannerisms are completely Orlesian - and so, perhaps, are his values.
We can't deny that the Orlesians would look upon a Ferelden devastated by the Blight, shorn of any defenses whatsoever, to be a land ripe for colonization. And we know that Celene is certainly always on the lookout for a way to add Ferelden back into the Empire, courtesy of Return to Ostagar.
Second, the whole Loghain recruitment debacle. The one where you find out if you executed him, it's only you, Alistair, and Riordan against the Archdemon? You seriously don't think that your Wardens wouldn't have pumped Riordan for information the minute they were reunited at Arl Eamon's estate? That is, if they didn't get all the gory details much earlier from Avernus, who would have no reason to hold back? The only reason Riordan only spills the beans at the last minute is for some cheap dramatic convention ("Oh, no, who will sacrifice their soul to the Archdemon? IT certainly won't be ME, the NPC that was introduced in the final act, ho ho ho!"). It's there that the plot breaks down to be completely unbelievable. I mean, seriously.
Finally, Riordan's idiocy leads to the entire Ferelden Coalition marching in the wrong direction, massing at Redcliffe rather than Denerim. When confronted about this monumental error (seriously, this isn't a "whoops, my bad" sort of mistake!!) he waffles about and says the darkspawn line is wide, or something like that. You're a Senior Warden, with decades of experience, apparently close to your Calling, and you make THAT kind of rookie mistake?! In the wise words of Cassandra, BULLSHIT.
Yeah, that's my anti-Riordan rant...