The equipment thing is definitely a good point. I was running around in the same armor for nearly thirty hours on my main character because I found something so insanely special that no other piece could really matched it. Had to spend some time crafting to make things a bit easier. It was never an issue since my mage and rogue do a great job of staying hidden during combat and the two warriors keep all the heat off of them. The only real difficulty comes from enemies who spam attacks like the dragons that hit the whole party or those damn terror demons who jump attack back line party members out of no where.
Also, I think my Solas has a fucking deathwish. He actually ran straight through the dragon's AOE lightning attack and died on the spot. I'm still cleaning the spit off of my computer screen after that particularly loud rage session.
Sometimes its best to set the AI off during the Dragon Battles and just micromanage them through the tactical view. This way you can move your ranged characters within the safe zone during a Dragon's wing attack and not have to worry about the AI being stupid and dodging right back into the damage zone.
I play an Archer Rogue myself because it turns out the AI handles rogues the least well of all the classes. Though a Party of 1 tank + 2 mages + Archer is pretty darn effective.
I'm quite happy that DA: I is winning so many game of the year awards, it deserves it. DA: I feels like my new skyrim.
Also, I'm not surprised someone could solo the game on nightmare with a Rogue Archer, its the most powerful class in the game. And stealth is the most powerful ability in the game.