From personal experience, some people prefer mic gain being the default scroll action, and some people want game/chat mix.
Either way we can't please everyone.
As it stands, game/chat mix is an Xbox only function. So it personally doesn't make sense for it to be the default action, whereas mic gain works for everything.
As mentioned by the Audeze account, it's not something that can be configurable at the software level. A choice had to be made, and considering the uses, I personally believe mic gain being the default action is the right call.