Wow this is going on a bit its simple really.
As a ppl you have been tested to the minimum ppl standard to see if you can be a safe hobbyist.
As a cpl you have been tested to the minimum cpl standard to see if you can be a safe commercial pilot.
Both types of pilot are expected to improve with experience and have allot lot still to learn its just the cpl has a more in depth flying training and allot more theory and a harder flight test due to the tighter standards required. This gives him or her a safer starting point than a ppl.
You cannot join the red cross and do a few weekends medical training and then do the work of a doctor even if you think you may know as much as one.