Does one need to be a pilot, let alone a "professional pilot" (whatever that means - school teachers alao claim to be in a "profession" but few doctors or lawyers think of them as professionals in a true sense, but it really is a bit elitist), to assess a person's flying skills? I would think that an aeronautical engineer, servicing aircraft and no doubt spending a far bit of time flying in them, might be able to express an valid opinion on how well someone flys the aircraft he or she maintains.
I do not mean to ****estir, but to suggest that a person can not express an opinion, or their opinion has less validity, because they are not a "professional pilot" is a bit unfair.