This game is not built to be difficult. It's too limited for that. The AI is pre-programmed and doesn't learn or adjust, the enemies are static and the cards are stacked on the PC side. The only thing programmers can do without a massive overhaul is make every combat a vomit inducing tedium fest of overdeveloped health pools and resistances. Adding another creature that you know how to fight isn't going to do anything, you'll adjust easily and then it's just time. They can throw crazy amounts of enemies at you, but people said they hated that back in DA2 so they have created static clusters of patrols instead. There do not seem to be any advancements in AI depending on difficulty, so all that you are left with is beefing the monster up. Which doesn't make it harder, it just makes you do the same routine for a longer time.
Well, AI in most games is quite static... I think some FPS games have their enemy AI setup with different routines based on the player character's range...but not too crazy. I can't remember the last game I thought had great AI.
Some rare fights are tough even for an early soloing KE, such as a Rift fight i just had with a Revenant, Arcane Horror and 2 Terrors and multiple archers. Those 3 demon types together can really rip you up! If bioware applied some of their AI routines to other enemies, it would be quite challenging. I ended up having to use Mark of the Rift for that one...I only had Cassandra with me in that fight, but anyways, considering KE solos most things, I was quite shocked.
Revenant has that grappling hook and sick melee damage
Arcane Horror has that ridiculous face melting torrent of spirit damage
and while those 2 are picking on you the terrors are knocking you on your back
A rare example though, it's very seldom to be in any sort of danger after Skyhold.