Hi Will,
Hmmm, looks bad! At the same time I think this damage could be repaired.
I think I have the same rudder blades (just the black gel coat version) Mine might be at least 5 years older than yours. My blades do not show this issue.
If impact is not causing this type of damage - have you considered sunlight(UV) - It looks like you tend to store the boat outside with the blades attached. There are several places selling coveres for hobie rudder blades.