By what measure are these games considered disasters? I was under the impression they were critically well-received and sold a decent amount each. DA:I was a better game than DA:O 2, for example (at least IMO).
Regardless, I fail to see what the engine has to do with anything, considering they both presented noticeable graphical and mechanical upgrades over their prequels.
Inquisition's development was a disaster due to poor tools. Pax 2013 demo, for example, was faked because no one knew what gameplay would look like(A YEAR BEFORE RELEASE), and it was mostly caused by missing engine systems. Game turned out to be OK though.
I am having a hard time understanding what the Frostbite engine had to do with any of this. Anything you can point to besides your opinion on the matter?
Seems to me the engine was perfectly capable of doing everything you wrote it can't do and both games were successful deliverables.
idTech would be great for Halo and Call of Duty. But it isn't great for The Elder Scrolls, Starcraft, Gears, and many different games Microsoft Studios are working on. EA already tried to make every studio to use Frostbite for every single game and ended up with disasters like Dragon Age Inquisition and Mass Effect Andromeda.