Not all mice have smoothing/processing. All mice have """interpolation""" though (not really interpolation, just subpixel motion detection) because otherwise speed related accuracy variance would be a very bad problem. All mice also have an update barrier at low movement speeds because otherwise either mice that are sitting still would have cursor drift or they would implement a real motion deadzone which is silly (and I don't mean what the MLT04 does).
Most modern sensors do have an extremely tiny amount of smoothing for some reason (why???) but in certain sensors and sometimes at certain DPI setting ranges it's small enough that the impact it has should be less noticeable than increasing your ingame sensitivity by 0.01% or something.