It might seem surprising to someone unfamiliar with Revit but it has not had a diameter dimension option for twelve years, since the beginning, only a radius (radial). That said, it has never prevented me from getting something done, just inconvenient at times.
In my view, any hole you make (or need to describe) with a drill is better dimensioned with a diameter value, you buy drill bits and core drill sizes based on diameter. More often than not I used text and a leader to "point" at a hole and say what diameter it needed to be. I didn't need a dimension for that.
Now for walls that are curving (or soffits or ceilings etc), those are better laid out with the radius. Give a contractor the diameter and they just have to divide by two anyway. In fabrication I used diameter dimensioning all the time. In construction on site, very seldom...unless selecting a drill bit.
So no diameter dimension for many years, but no more...Now it does!
One place I will be very grateful for the diameter dimension is in the family editor. What was dreadful was defining pipe diameters there without it (or round duct fittings for that matter).