You need to rewatch that Killzone 2 announcement trailer...
Edit:
So I'll elaborate on what I said:
The Anthem trailer looks about as good as the game running on ultra on pc.
The difference is in the density of effects and assets. Essentially it runs at in game cinematic levels of detail, but is very much seems to be the game engine running.
The same can be said for Watchdogs, though it was certainly worse and here you could talk about false advertising.
There can be many reasons for this, maybe they couldn't get a stable framerate, or maybe it was just too labor intensive to build the whole game to that level.
The Killzone 2 trailer isn't Killzone 2, it is a proof-of-concept CGI cinematic probably made by the same guys who made KZ1's intro.
The geometric detail, the high resolution volumetric effects and the insane texture quality wasn't possible on any system back then, and certainly not the PS3.
The "demo" was never a game, it was never a game engine, it was never running at 2fps on a devkit or anything like that.
In conclusion, The cutbacks seen on Anthem and Watchdogs are reasonable given time constraints and the need to have a similar product on all platforms.
The KZ2 demo was just fantasy.
(I would like to add that I very much liked KZ2, and that it was a fantastically good looking game when it launched).