Even with just RPG's , shooters and the like , there can't be too many. Games take a long time to create and if you don't want Gears 1 , 2 ,3 ,4 ,5,6 ,7 or Halo 1,2,3,4,5,6,7 and so on or Horizon Zero down 1,2,3,4,5,VR or Spiderman 1,2,3,4,5 you need to have a lot of teams working on a lot of diffrent ips in each genre to break up the staleness. MS's other franchises that they grew or purchased can now have more time between releases to be better products and keep them fresh.
There are other companies I'd rather MS have bought before this but MS wanted Activision for its IP's , Dev teams and mobile foot print