Basically, the fighers are ineffective tanks against groups unless you have a dedicated healer, but then now you have a mage taken away from offensive spells.
It seems like mages rule here. Unless your team is overly stacked with mages you don't have a chance.
Rogues are equally pointless. They cant even unlock chests until they hit a decent level. What's the point in that?
I'm going to have to disagree about those three points. I'm running a double rogue group (pc + Leliana), Alistair as tank and Wynne as healer/support. I don't use cone of cold, force field or whatever the common mage tactic the kids are using. Morrigan tends the stew pot at camp. Wynne only has the dps spells she came with when I got her. The only AoE dps I ever use and only against multiple high armor targets are the flask bombs that my rogue makes.
My suggestions would be:
1. Never allow the mobs to dictate the battlefield if you can help it. You can pull, line of sight their ranged, make them come to you. You have to take away their advantages. If I cannot make line of sight pulls, I have Wynne disrupt the ranged with earthquake.
2. Learn to pick out and eliminate the most dangerous target(s) first. In this game I usually find them to be enemy mages. I position my rogue to intercept/or behind the mage, have my tank make the pull and my rogue makes sure that mage is well on its way to a long dirt nap before it gets off a single spell. Second to that are sword and board mobs. A pack of them will chain stun your tank(s) from full health to dead. I coped with that by making careful pulls, ccing what I can, and even letting the aggro run loose a little bit. If my tank gains aggro too soon in those pulls, he gets dropped like a rock. Real threats get picked out and focus fired by my guys very quickly. Pause function lets you assess what you've got in the pull, make use of it.
As an aside just because a mage is a healer doesn't mean all they do is cast heals. Next to my rogue, the person I micromanage the most is Wynne. In between her healing cooldowns, she deals out offensive and defensive buffs, rolls out some earthquakes and stonefists if necessary, cc with paralyzing glyph and assists on my rogue's target with staff dps (lol, hey every bit helps) and arcane bolt if needed. I mostly pick up healing spells on her, but she is always doing something. The same goes for the rest of my party members. I do micromanage the hell out of my party sometimes, but they are rarely ever idle and things die quickly.
It would help if the game has a combat log so you can see what's wrecking you, but since it doesn't you do have to pay attention to the scrolling text above mobs' heads. When you see a pack of red circles heading for you, yes they're all gonna die...but you have to learn to dictate when. Not all red circles have the same priority. If you're getting overwhelmed quickly and often, you have to find ways
of controlling the incoming damage while directing yours or you'll get
continously rolled in this game.
While you are mostly outnumbered in this game, unless you are terribly
asleep at the wheel you should almost never be outgunned. The sum of your
group's abilities + your brain are always greater than that of the mobs you're
fighting.
Good luck!