I would say scallop was the right choice, as it gives a uniform surface stepover, giving a consistent finish quality from flat to nearly vertical.
Morph spiral is useful for arbitrary regions that are somewhat round and within maybe 45 degrees of level. Further from level gets poor results, as it tries to use near constant stepover in x-y, rather than on the surface. Elliptical, amoeba shaped, whatever. Regular spiral doesn’t do a great job if the region isn’t basically circular or annular in profile.
Better finish can be achieved several ways:
Using a ball end that is larger radius or smaller stepover. There isn’t a lot of benefit to a stepover less than 1/4 the ball end diameter, with the smaller diameter tools. Use rest machining with smaller tools and correspondingly smaller stepover to get into the corners.
Using a consistent surface angle and using a vee tool with a matching angle. This can be a bit difficult, as very small issues with machine calibration, squareness, or tool angle will leave hard edges in the work piece that can be tough to get rid of.
What ever you do, you will not get a perfectly smooth, mirror surface. I would final finish with 400 grit wet-or-dry (wet, with kero, WD40, alcohol, or other thin coolant) on a wooden mandrel (flat for the spokes and convex, slight radius for the concave) to take the scalloping down, then your choice of final finish (finer papers up to polish, scotchbrite for a buff finish, scuff with courser paper, whatever)