That was a single. F*ing. Demo-zone. Made specifically for the show. Same as with most of the early pre-alpha demos, it had nothing to do with the final release. You have no proof that your 'new gen' could have handled such things well in reality, and you also have no idea what that next-gen-release-that-never happened could look like. Also, here's a post from the GameDev about what those show demos normally are.
There is no 'new gen'. It's current gen, now. We're two years into it.
But anybody with even a basic understabding of PC gaming knows this to be true. If you populate an area with more NPCs, objects, pathfinding scripts than the hardware can cope with comfortably the framerate drops dramatically. And often to unplayable degrees.
DAI is running in an engine designed for current gen systems. Not for 360 or Ps3. In order to have the game running comfortably on those systems things had to be dumbed down and whittled away.
And despite what many people may believe it's not as simple as "but if other consoles or PC can manage more stuff on screen just LET them."
When you're making a multiplatform game all platforms have to have relative parity. Because that way if a bug happens in one area of the game you fix it on all platforms with one fix. There isn't enough time to treat diffeent platform in totally seperate ways, unless you outsource a platform to be a Port of the game created by a seperate company. As was done with Dragon Age Origins.
So, yes. By developing last gen along with current gen it will have had a negative effect on the game. It will have limited how the game world was populated. The limitations of the old hardware then become limitations for the product on better hardware.
Just as console versions also tend to limit the standard of PC games 'out of the box'. And why modders work tirelessly to get the best out of PC games, beyond the original vanilla versions of a game.
While I agree with your sentiment, I am still glad that it was made for PS360 or I would never have been able to play until much much later.
And I'm glad you got to. It's just a shame that you're now only getting half the experience of the full game's life cycle.