"...the porphyry- should still have the highest mineral concentration."

Indeed, I am not a credentialled geologist, but to my understanding, the difference between porphyry and skarn/CRD is that they evolve from two different geological events, one after the other.   

The event you describe as forming porphyry happens first and in sedimentary rock.  Skarn/CRD ores form as secondary events related to more intensive dry or drier heat.  They add minerals or concentrate ones already there in a metamorphic process.  Superheated waters are essential in forming porphyry, but not so much so for skarn/CRD.  Of the two, skarn/CRD is richer.   

Then, there are hydrothermal, epithermal, and mesothermal mineral concentrations, but let's not go there just now except to note that porphyries are hydrothermal, skarn/CRD are not. 

VP