That's a good point about the age of the survey even when it was circulated - and it does raise the issue of why a marketing department would *ever* ask for feedback about something that was confirmed to not be in the game.
I have an issue with developers saying that the information is old, though, because - not to sound too conspiratorial - but of course they'd say that. It's what Ray and Greg said about the leaked ME3 script, and that was 100% the same as in the final game. If the timelines for DA:I were as tight as David suggests above, then I think there's little that could have changed about those characters at that point. Even if dialogue wasn't written or their final concept nailed down, the processes for them being in the game - all the thinking and planning - seemed to be over. I just think the pipeline timeframes (for art and writing, especially) are way too long to change things on a whim.
And about the survey:
It wasn't released so much as leaked, by people who were supposed to be doing a confidential online marketing survey. They deliberately broke confidentiality agreements to take screenshots and post them on the old BSN. The survey site added users' IP addresses to the companion art images, for example, which is why all of those old pictures have a big black bar in the middle. I'm frankly astonished that people thought Bioware fans *wouldn't* leak that sort of information as soon as they saw it (though I strongly disapprove of breaking confidentiality agreements like that), and the survey clearly had no anti-copy measures built into it.
The information was never intended to be public, and if it hadn't been leaked like that we probably still wouldn't know who the Grey Warden, Sera, or the Iron Bull were. Inquisition's marketing, it has to be said, are still teasing characters like the Iron Bull as though we don't know who he is - and for the vast majority of Inquisition's future players, that's still true.
But it has to be emphasised that Bioware did not want that survey to be public, and for a long time the survey content had more information about Inquisition than any official source.
(Some might say it still does, given the hints about co-op/multiplayer modes, Cole/Dorian/Sera/the Warden and the general plot outline of the game.)