I understand your point. I believe that approach would be impractical with all the cruise line changes. You are suggesting that when Princess decided to add a surcharge for Casual dining, add a mandatory gratuity on the speciality dining fee, add a charge for Medallion shipping charge, increased the cost of internet, etc. that Princess should keep track by individual and implement the changes by individual booking dates? No freakin way, especially given all the changes.
IMO it is more reasonable to increase the price of individual optional extras, than increase the base price for everyone. Some people do not want all those optional items.
The fact that Princess allows you to pay an extra $10 a day pp to upgrade a package seems like a fair and reasonable approach. Customer’s decision.