Raising the gain when you are using a power law gamma reduces the dynamic range because gain is a multiplier. If you multiply your 0 to 100% input range from the sensor by 2 it becomes 0 to 200%, but you can’t record 200%, you only have room for 100%. So you have a small change in the shadows but a much larger change in the brighter parts of the image and the dynamic range that can be recorded is reduced by 1 stop for every 6dB you add. Adding gain means you will clip earlier. If you stop down to compensate, bringing the highlights down to where they would be without the added gain you reduce the shadow range as the SNR will become worse, and the extra noise from the amplification will limit the shadow range. You gain no additional highlight range, you are simply returning it to where it would be without the extra gain, but the shadows suffer. With added gain the highlights are less pleasing because the gamma curve is designed to work with the sensors output range, when you add gain because you can now more easily exceed the recording range the highlights clip sooner and don’t look as nice as a result.