Radar and Mirror serve different purposes.
The radar is for your blind spot, mirror for what happens behind.
The mirror is useless in a corner side by side, that's where the radar comes in to stay clear of the other car.
The radar is useless to see how close the car behind is, which side he is going and whether he brakes on time.
You need both.
In VR you can glance over or see the other car from the corner of your eye when side by side. In bumper and roof cam you can't see what's happening beside you. In roof cam and chase cam you can't see what's happening behind you. But it is easier to see what's happening in front of the car you are behind. In bumper cam you have to keep a little distance and naturally get out of the draft of the car in front before the braking zone so you can see where you are going and what's happening further up front.
I suspect those that ride right on your bumper are not using bumper cam. When I'm that close the whole view is nothing but the bumper of the car in front of me, driving totally blind