The software landscape has changed. Everything you've said was true for previous consoles, but doesn't stand any more unless the consoles pull out a special hardware bonus.
so at least we do agree that in the past a lot of console games launch titles or second generation titles had an advantage graphically over PC games. (Ridge racer for ps1, Mario64 for N64, soul calibur on dreamcast, gran turismo3 on ps2, Halo1 on xbox1, gears of war for xbox360...)
But we disagree if yes or no this historical pattern would continue in the future for nextgen consoles (ps4/xboxnext).
Wait and see who would be right in his predictions ! just remember that you hear it from me first : evolution studios nextgen game for ps4, naughty dog, santa monica, guerillas killzone4 and a glimpse of Gran Turismo PS4 would destroy anything multiplatform developers would show this E3.
I'm not saying your wrong, you have some good points but there are other things to be considered which make the situation much less clear cut. We can't just assume this time that first party exclusives are going to look better than multiplatform games from big development houses using well established, highly supported DX11 3rd party engines.
Its not just about the engines, the engine is important but what is more important is game assets (textures, lighting, polygons, animations...), with least powerful engines you can produce a more graphically impressive game if your game assets are of higher quality.
Of course a better engine / more powerful hardware, allows you to use higher quality assets, but it is up to developers to decide how they want to implement their own assets. generally with multiplatform games, developers are forced to compromize, using the assets that suit best most platforms and not only one particular platform, which could result in overall less impressive graphics compared to exclusive games.
As I said previously, Gears was built on a multiplatform engine this generation and is touted by most as the best example of that generations early graphics. Microsoft paid for it to be 1st party but the engine itself could just as easily have been producing games like that for the PC or PS3 in the same period. Exclusivity there was a business decision, not a technical boon of working only to one specific architecture.
gears of war was an exclusive title for xbox360, it dosent matter if it is developed by the same multiplatform engine or not, as i said the fact that you develop exclusively for one console, you will tailor your game assets and ideas to the strength of that particular console.
(for example for xbox360 : higher rez transparencies, more complex vertex shaders (you can see real applications of all of this in Halo4), for PS3 : more complex pixel shaders, more complex physix and animations calculations, more complex lighting engine (you can see the evidence of all of this in Last of Us).
I just said : console games look better in the launchtime of consoles, and by the time PCs catch up and surpass consoles (crysis was an anomaly in that regard). why is that ? because console developers put more effort into harnessing the new console hardware, PC developers on the other hand cant create games just for the sake of the hundreds of gamers possessing high end PC, they can only develop for the least common denominator, by the time the lest common denominator becomea lot more powerful than consoles, PC developers can than create advanced graphics for PC (half life 1 in 1998, Half life 2/doom3 in 2004). 