Agreed, they were trying to do that with Marathon, but people got all weird about it. Halo Infinite tried some different things, still trying? Infinite flopped hard on PC because of the high aim assist for controller players in my opinion. There's no way to be competitive (consistently) using a mouse in that game.
Giving mice some tracking would pull some of the bottom players up, making most regular players just a tad more consistent (especially with networking hiccups, frame drops, visual clutter, etc.), and probably would have ZERO impact for players at the top, 1.0% - 0.01%.
Plus, values could always be tweaked.