I'd like to point out the current situation of Xbox Biggest Franchises.
I think this is very relevant to the thread, seeing how the Xbox One in order to stop the Switch gap to grow it need System Sellers to increase the sales. As soon as possible.
Having discussed this previously with other users, i would like to extend my original point.
Xbox Big 3 is on a sales decline, as i will show right now:
HALO
Halo 1 (5.5m) < Halo 2 (8m) < Halo 3 (12m) > Halo 4 (9m) > Halo 5 (5m)
GEARS OF WAR
Gears of War (6.09) < Gears of War 2 (6.75) > Gears of War 3 (6.21) > Gears of War 4 (3.05)
FORZA MOTORSPORT
Forza (1.05) < Forza 2 (4.05) < Forza 3 (5.49) > Forza 4 (4.57) > Forza 5 (2.31) > Forza 6 (1.99)
I underlined the peak of each franchise and the subsequent Factual Decline in Sales and Popularity with each iteration of the game.