The way I’ve always seen it, and I see it in MCC as well, where mouse aim isn’t nearly as janky as Infinite (mind you neither is controller aim) is that Halo is both a game where the first shot doesn’t win a gunfight, AND where movement isn’t so crazy you need to keep up.
KBM accels at games where shooting first is the primary contributor to victory. Think very short killtime games, Battlefield, CoD, CS etc. That’s because the amount of time it takes to snap your aim onto an enemy is much shorter, especially for enemies that you aren’t already facing.
KBM also has a very clear advantage in extremely mobile shooters, classics like Unreal and Quake, or modern games like Destiny come to mind here. Because even with aim assist in place it’s extremely easy to lose track of players in these games if your reticle speed isn’t essentially uncapped.
Halo is different from these games. It’s a game with both slower, more predictable movement AND where the first shot in a gunfight is generally less valuable than what happens after. This gives a controller with a comfortable aim assist mechanic plenty of room to both compete with and surpass M&K. Infinite in particular went to great lengths to nerf controller compared to the rest of the franchise, by making the aim assist significantly less comfortable, but it is still something players could get used to with practice. And adding some bullet magnetism to M&K could result in the input becoming so easy to use that it practically removes the game’s skill gap.
It’s kind of a -Yoink!- of they do, -Yoink!- if they don’t situation. Removing aim assist entirely, or further making it uncomfortable on controller is plain not an option. I think most controller players would advocate for it to be restored to the standards of the franchise. I.E. making it feel like MCC. And at the very least, certain weapon mechanics should be tweaked so they feel rewarding for M&K players. BR should have it’s spread completely removed, and Sniper should have both it’s unscoped negative AA and spread removed for example. The Sidekick could also stand to have it’s rate of fire slowed to match the current “paced shot” RoF (the RoF it has when you wait for the reticle to unbloom between shots) it could then stand to lose a shot from it’s ttk, becoming a 6 shot kill instead of a 7, just to keep it’s optimal TTK as close to what it is now as possible. The bloom effect can stay, but it would act like a rate of fire timer instead of an actual accuracy mechanic. They should do this to the Sniper as well, like it was in 4 and 5.
Changes like this would go a long way towards making weapons feel equally viable on both inputs, making controller play feel more natural and M&K play feel more rewarding WITHOUT damaging the skill gap of the game.