Half-assing fights throughout DAI's mid/late-game is completely possible, as was in DAO with its unlimited potion slogging. I noticed this was mainly due to being able to fast travel to camps to regenerate your zone potion stocks or alternatively the very frequently placed supply caches in dungeons.
One solution towards increasing challenge is disabling fast travel to camps once you've reached a zone or removing most dungeon supply caches. The difficulty of the game would skyrocket ESPECIALLY towards the late game when you're at risk of one shotting your allies assuming you have friendly fire on (and you should if you have it disabled and are concerned about difficulty).
This would massively increase difficulty for those who don't want such challenges as well though, so this should be limited to Nightmare or even made into a "Hard Mode / Survival Mode" toggle upon starting the game or something.
It would be relatively simple to mod in as well in theory, assuming it can be at all.