The offset is not about dynamic range. It is about preventing pixels clipping to black because of noise.
Using the ASI1600 as example, at gain 0 you use offset 10, at unity gain you use offset 21 and at gain 200 and over you use offset 50, all not to clip pixels to black.
Most users use unity gain or lower to shoot LRGB, but as soon as NB filters are in the chain you might want a higher gain/offset combination.
But with the Ascom driver you can not change the offset for an event within a sequence. You can’t have LRGB and NB in the same sequence unless they use the same gain. And you don’t wont to use different gain unless you can change the offset correspondingly.
I would not mind if the offset was dynamically set in the camera and we would not have to think about it. But until it is, we need the possibility to set both gain and offset pr event.