Bose, If you care to re-read my post you might notice that nowhere do I imply that a CPL holder is a more skilled pilot than a PPL holder. I simply stated that the instructor course should be about learning to teach, not brush up on flying skills. If I am wrong, perhaps an FIC instructor or FIE can post here to put me right.
As you are obviously so clued up about the difference between the CPL and PPL skill test, I assume therefore you are both a PPL and CPL examiner. True or no?
Likewise regarding theoretical knowledge, my post clearly states, "if all experienced PPLs who aspire to instruct really knew their stuff, CPL level of knowledge wouldn't be required." Perhaps you can explain, using a whiteboard and four colours, why that is wide of the mark?