I'm not sure if 100% understood the second sentence, I think you're talking about how scrolling the screen will move the mouse along with it? It might be interesting to experiment with an option where the mouse cursor stays still (relative to the game world) when the screen scrolls, but I think something like that would be less than ideal for anything except a relatively small boss arena.
This is totally a nitpick and I feel silly dwelling on it, but the boundaries of the arena are close enough to the boundaries of the map that scrolling stops when approaching the corner of the arena, changing the player's targeting angle as they move around when aiming with the mouse. Just wanted to mention that during my playthrough, it was my motivation for switching to gamepad input (which ended up working really well).
Looking at the behaviour again today, I see that there is more going on with the camera than just keeping centered on the player, like the focus mode expanding the zone that the player can move in before scrolling occurs. (And losing visibility on the boss because they're out of frame would be a worse trade-off.)