Well, since the Zhuge 2016 number 70m numbers, 3 Halo games have released, Halo Wars Definitive Edition, Halo Wars 2, and Halo MCC for PC, plus we would have had continued legs for mainly Halo 5 and MCC for Xbox One (Halo 4 and older Halo games wouldn't be selling much by that point).
Michael Pachter claimed in 2017, a year after the last official Halo 5 five million+ number, that he was told by somebody at MS that Halo 5 lifetime sales were trending towards the bestselling games in the Halo series, so most likely 8m+ by that point. So, I'm going to guess the breakdown of those 11m sales from 2017 to now is something like this:
I can be wrong here but something tells me that MCC sold more than Halo 5, just considering the PC release in the first place. Going by your suggestions Halo 5 sold 4.5m on Xbox while MCC sold only 1m. Doesn't seem likely as MCC had only one year headstart over Halo 5.