This is not necessarily true. While I have never needed to make a claim, my understanding is that Parcel Pro doesn't care what value customers place (for Customs purposes) on the parcel, and they will cover the insured amount whether or not there is a disparity.
As to the primary issue being discussed, I suspect that companies like DHL made a conscious decision to add dubious fees, rather than pushing the advertised price of shipping even further skyward.
FWIW, while I have lived in Europe for a number of years now, I imported many watches into the U.S., and found FedEx to be far superior to the other courier companies with specific regard to their Customs 'program', and any help needed during the process. Sadly, I believe that their service, at least in Europe, has been degrading for some time, and I should also add that in Portugal they now tack on a €45 charge for their (incoming) Customs processing service.