Cecilia, when you finally cure your cracks?
First, they looks disgusting and indicate a negligence and a lack of your care.
Second, the cracks have the very thin skin on their bottoms. Such thin skin can be easily pierced by a small stick, needle or a similar foreign object. Such damage can lead even to the sepsis, especially if a small fragment of that object still present in wound. The cracks also can bleed. So the cracks are not the sign of strength and endurance, they are your vulnerabilities.
Third, the cracks are difficult to cure.
If you do not want to lose strength, how about treating skin only on an edge of a heel?