When I look at this tactically dead games my preference is for the ability to fail. DAI offers a lot more chances to fail than DAO ever dreamed of. DAO does offer a richer variety of guaranteed win buttons for those for whom that is their jones.
DAI offers a lot more chances to fail? Seriously? In the terms of combat or during the story portion of the game (being kicked out of the Orlais Ball for example)? And a richer variety of guaranteed win buttons? 
Ok, DAO had Force Field, heals, gazillion of potions, DW Warriors, all Archer/Mage party with Shale, Mana Clash, Wynne, immortal Arcane Warriors / Blood mages that could solo the game with ease (but they required some basic timing for switching BM off, healing themselves, etc).
DAI has Barriers, all Mage party, all Archer party with a Mage. immortal Champion Warrior, focus abilities, the Templar combo, 2 aoe healing potions, Full Draw, Hidden Blades, Mark of Doom, guard on hit for every class, heal on kill for every class, heal on hit for every class.
And then we have the famous Knight Enchanters, that unlike DAO's Arcane Warriors don't require any timing or any planning when to use a ability whatsoever, you can literally just bind 2 abilities to your keyboard and play on it like a piano. 2 abilities, without any thought when to use them, even against dragons.
And the most OP thing any DA game has ever seen is the Tempest. His gatling gun ability Flask of Lightning or the combo of Flask of Fire + 4 Leaping Shots alone would guarantee him a place among the most OP classes. But then there is Thousand Cuts. An ability and I kid you not, that can instakill ANY enemy in the entire game on nightmare. I was on the same level as the last High Dragon in Emprise du Lion and his 310k HP were gone in less than 5 secs without my party doing any dmg. And if that was not broken enough, you can use this every 32 seconds.
I am sure I left out many OP things in both games, it is not an exhaustive list and I don't have the time to go through DA wiki and check every class. I just posted it to show you, that in DAO there is not really more win buttons and when there are, they are not as ridiculous like a class that can be played solo by sitting on a keyboard or a class able to instakill all the things.