Judging from last gen I doubt there will be parity. We have seen countless games that ran better or had different resolutions. And exclusives will look great on either of the consoles. History repeats itself. We'll see games with slightly different performance, Xbots boasting about spec superiority and Ponys calling out lazy devs. Unless you can tell me a reason why it would be any different next gen.
Simple. That was a 40% gap last gen at a much lower res(900p-10809), this is a 15%-20% gap this time around at much higher res(2000p-2160p). While it will be there no doubt, it will go unnoticeable for the most part. I actually see more xbox fans complaining why there isnt a gap in third partys games.
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