Parcel dimensions are weights are important because the actual shipment cost calculation is based on cubed dimensional weights. So the package dimensions are important. It's a bit of an international thing between all the major couriers and post services. Normally the calculation is:
DHL: (L cm x W cm x H cm)/5000[2] or 4000[3] depending on certain import/country criteria
FedEx: (L cm x W cm x H cm)/6000 (new) or /5000 (old, still used in Asia) for international shipments, (L cm x W cm x H cm)/7000 for domestic shipments
UPS: (L cm x W cm x H cm)/6000 or /5000 depending on certain import/country criteria
The final change is based on the higher number of the actual weight or the dimensional weight.
Don't get me started on fuel surcharges.
Tracking numbers are can be large for a variety of reasons. Unique values being one of them but some companies keep them know for multiple years. And the numbers are assigned per piece you are shipping.
You make a lot of good points but the reality it all these companies make their money from corporations. And corporations for the most part automate the hell out their shipping solutions. As for the courier companies, every time they have to deal with a bad label or anything that requires a human to step in to help process the shipment you are slowing down the production line. Watch a couple videos of a Fedex or UPS sort facility to get an appreciation of what they deal with daily.