I made zero effort at trying to learn any for of tactics in DA:I, and it worked. I never died once in that game (played it on normal). Someone told me Barrier spell was all I needed and I tried it out. They were right. Try it the next time you play through the game. Barrier + whatever + the odd Focus when you get that ability.
How did you knock down those dwarven assassins or shrieks that spawn right in the middle of your party, though? Did you turn the friendly fire off?
Well duh. You installed a mod that lets you cheat. No wonder the game got easy.
If you only play to power-play, then yes. Most spells are "useless". For roleplaying reasons alot of them can be quite good. And it is more interesting to play a character that has a weakness or two too.
Not saying DA:O was a difficult game to play or learn, though. But it did require a bit of effort on the player's part to get into the system and things like that. Setting up your party's tactics was pretty important too.
So now we've gone from auto-attack and barrier are good enough on nightmare to auto-attack and barrier are enough on normal. I'm sure normal is a joke difficulty. But normal on DAO is also a joke. Perhaps harder - especially pre-nerf - but not "hard" or "tactical" in my view.
By the time you run into enemies that spawn into your own cone (i.e., during the Deep Roads) you have glyphs of paralysis and - more importantly - access to either or both of mass paralyse and blood wound. With blood wound alone these enemies are a joke.
If you're talking about RP reasons now we're just getting into the self-nerf. Any game is hard if you nerf yourself.
DAO didn't require more for me than using choke points, 3 mages, direct damage spells from the elemental tree, mass paralyse and glyph of paralysis and one BM/SM PC. That's it.
I also never used tactics (edit: I mean preprogrammed abilities; I used tactical planning but I do that in DAI too). The greatest source of frustration I had in DAO came from not realising what the disable tactics button did until late in PT#1.
Eventually in my later PTs I caved and automated healing use at certain health thresholds since that kind of baby sitting got boring but then I realised this meant activating AI target and auto-attack behaviour.