Halo Infinite is not interested in accusations of aim assist or helping one side over another. Streamers like Herschel 'Dr DisRespect' Beahm and Michael 'Shroud' Grzesiek have mentioned how unfair it is to play with controllers. Controller players have stated that aiming with a mouse is as easy as aiming with a controller.
Instead of balancing the two, Halo Infinite decided to separate them in ranked modes. Shroud himself suggested this, showing that 343 Industries is listening to streamers. Yet, there's no telling how the community will receive this at large, which generally likes cross-play.
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Halo Infinite cross-play
Casual modes and games are still available to be played with friends who use different outputs. This decision is for players who play competitively or ranked. In this way, everyone is treated fairly.
My friends at Esports Talk made a video highlighting the bigger aspects of this change, seen below:
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The issue has everything to do with the debate over aim assist that has raged since cross-play became more prevalent. Many players in Apex Legends, Fortnite, and especially Call of Duty have complained about unfair advantages. Halo Infinite has three ranked modes, so that argument is moot.
There is no telling how many streamers will complain that they can't play ranked with friends who use different input methods. A pair that comes to mind is Nicholas 'NICKMERCS' Kolcheff and Timothy 'TimTheTatman' Betar. TimTheTatman has started to learn how to use a controller, but he prefers a mouse and keyboard, while NICKMERCS prefers a controller.
This may be a reason for streamers not to stream Halo infinite as much, which would hurt the game.