From 360 onward, particularly the second half MS handled their first parties poorly to say the least and they are now paying for it. The 3rd party titles were selling much better on 360 than PS3 and for some reason MS had it in their head that come rain or shine, that would remain the case going forwards. That did not happen, most 3rd party games sell better on PS4 than XB1 so that's already a huge reliance they had gone.
Then their treatment of first party franchises was beyond fucking stupid, I mean damn what were they thinking? Halo, Gears, Forza, Fable and that's about it, sooner rather than later those franchises were not going to stay on top of the game. Halo has gone downhill to the point that it's at the level of say the Uncharted franchise (which is good but not outstanding), Gears I can't say yet, Forza always relied on bundles and Fable is dead.
Sony have not been great this generation first party wise but many of the studio remain, which adds diversity to the line up. Uncharted 4 looks to be doing well, GT Sport will do well, I'd think God of war should do well and Horizon could end up being big. All those titles I mentioned should do 4 million WW with ease.
The fuck MS got?
