I’m assuming you are aware that on the “Home Screen” (where the 4 horizontal bars exist) you can swipe from right-to-left to see radio control buttons there, yes? That said, you mentioned having the Map view there and obviously in that view if you have Navi running it shows arrival time/etc but does NOT show the actual map. So to that point, you’re correct, there is no way to handle that.
However, one of my FAVORITE things about the XC40 compared to the 80+ other cars we’ve owned, is that it has actual knob for volume, play/pause button, and prev/next track options. There have been a few cars of late (Tesla, etc) where you don’t get physical buttons like that. Based on the perfect location in the XC40 (better than in the Polestar 2, which lacks the prev/next track buttons BTW) — i find that adjusting volume, or skipping a track, is as easy to do with me down in front of the gear selector, as it is on the steering wheel, and use both interchangeably.
I think the concept that having more controls on the screen makes sense only, as you put it, the ability to co-exist. Navigation + radio controls should be easy to see at the same time, and once our XC40 screen gets bigger to match the Polestar/etc that should be a no brainer. I just hope Volvo continues to keep physical switches (like Hyundia/Kia are doing, but places like Porsche, Are not)