I just purchased my G80 yesterday and have used the Genesis app a few times. It works but the contrast is bad. It is very hard to read since the text is very small and the lettering almost appears faded. In time I will know what each icon means but it would be nice if the icons and text were larger and brighter. The dealer also had a difficult time reading it. The app itself works for me though.
My experience with most screens is the only adjustment for brightness is what's already easily accessible by the user and that's quite limiting. Maybe over time Hyundai will release software updates if they want to be proactive about improving this experience. Could always try emailing them, the more voices are heard the more likely something will be done.
Only thing is you have to make sure to get a case number or just some way to track it and have a paper trail. Often with big companies there can be miscommunication although there shouldn't be. Just have to do all you can on your end.