1. They could have held off the blight until the armies from Orlais arrived with the grey wardens of orlai thus hindering the blight from spreading and taking lothering etc.
2. I think Alistair makes a better ruler tbh.
The battle was Cailan´s idea, and the RtO DLC leaves clear the battle was lost even if Loghain had not retired. I have to agree there, as I don´t think such a king was worth the lives it would have taken to save him. I lost all respect for Alistair when he murdered the witch in Silent Grove, becuase his father had chosen to honor a promise he had made.
Anyway, I guess we all find characters we can´t let away with something. Yaevinn in Witcher 1 talks several good points, but if you´ve read the books you know more like he really is. Metagaming as Geralt didn´t know, but kill the sob anyways.