Are you a logician? I agree that that is a false premise. DAI is not a failure but even people who enjoyed it acknowledge that it tried to do too many things at once and failed at THAT task, which still does not make the game a failure but it takes a lot away from it. Most people play games for specific reasons not to get a taste of everything; they play Bethesda games for sandbox, Ubisoft for action and BW (in theory) for character driven story. They tried to do too much, almost as a hypercorrection of what had occurred with DA2 but they overshot in this correction, however it is still not too late for a flawless DLC. We shall have to wait.
How could we objectively measure that it failed at THAT task (doing multiple things) because it tried too many things at once?
As I said, the multiple things it does is something that I feel makes the game better (does it do them perfectly? No, but in trying, it has done better than the previous linear entries, in my opinion - and DAO and DA2 were both games I bought, enjoyed, and played on multiple platforms many, many times, and own all the DLC for on multiple platforms, etc). There is still room for improvement, but that's true of all games. I think DA is heading in the right direction; you disagree. Neither of us is wrong or illogical.
Personally, I play RPGs for a combination of immersion, roleplaying/freedom and excellent story. Fun combat helps too. To me, this is the best game for that except Fallout: New Vegas. And it was really close to edging that one out too. I felt DAI gave me a character-driven story. In spades. So when you say it "failed" at that, I wonder what your basis of evidence is. You can make a case that it failed to deliver that to you, sure, but when people present the "doing too many things" as objectively bad or say DAI was hindered by the open world, I simply disagree. I think it was an excellent evolution that will attract more people than it will turn off.
Can they make improvements? Absolutely! But I wouldn't say it fails or stumbles, as is.