Second Son looks on par, if not slightly a little better than the E3 2013 trailer of Watch Dogs. There is no reason it should look like a PS3 game on PS4. This just might be the biggest bait & switch ever done.
One would think Xbox One development gimped the visuals in the game, since every previous footage was on PS4 before a glimpse of Xbox One version was shown. But I'm going to go ahead and say it's probably a mix of both Ubisoft's ineptitude and XB1 development.
Once. Fucking. Again:
No. No it is not. Neither is the Wii U, nor Xbox 360 or PS3. You know why? Because Assassin's Creed IV was on all these systems too, and it looked amazing.
Did the same AC:IV team develop Watch Dogs?
Some overlap, but no.
So it's down to the development team's ineptitude, instead of any hardware holding the game back.