Shooters will always have a better attach rates on the XB1. The core fanbase of the XB1 is shooter fans.
The PS4 will have a better sales gap in games like Shadow of Mordor, or GTA, or had they not f'd up AC:Unity that too.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut