Maria Caliban wrote...
3. Even on the easiest difficulty, there are fights where their AOE spells are nessary, such as the 'back alley' bandit quests in Denerim.
Honestly, you must suck at building characters. I did those encounters with different companions in four games. On hard difficulty. I only had a mage with ae spells in only one of those encounters. For the love of all that is holy, don't stand in middle of the ambush site with archers pelting away at you. That would be stupid. Instead fall back around the nearest corner and make your stand there. It makes the archers either stay where they are, or come to you, and they tend to flock together for your melee ae abilities. Whirlwind - dual strike - bombs - traps - whatever.
Rogues -- If you have stealth, lay traps all over the place before the fight. Throw some bombs during the fight.
Mage -- if you have forcefield you can cheese your way past the difficulty of the encounter. Have your warrior trigger the ambush, let him draw the targets near him, and then cast forcefield. All the enemies will keep hitting him. Then you can peel the enemies off him one by one until they are all dead. And by Andraste's blood, put your companions on hold mode, otherwise they will tag all the critters off the warrior.
All that being said, ae spells do make life easier. They are not however as you put it, mandatory.