The game should allow OTS aiming and attacking with a mouse and subpalette usage with a keyboard even if the user's main control method is a controller. As we know, controller controls are rather sluggish when compared to K&M in those two specific functions, and I believe it isn't hard to code in combined functions. Many people play with a controller for the extra comfort, menu navigation and (most importantly) slow walking animations, and honestly I think this should be done to enhance their experience.

The game does allow it, both on the PC and Xbox; in fact, it is the easiest way to use the subpalette with controller (made especially easy when using a non-official chat pad, which is basically just a mini wireless keyboard attached to the controller), and I also regularly use my left thumbstick and mouse in tandem when using seated weapons (like turrets, harpoons, etc.) with no issue. Mind, to get it working, you need to make sure Direct Chat is disabled (either through the menu or by hitting the Scroll-Lock key), and there may be another setting for making sure that the mouse controls the camera and not just the cursor.