StephaneD,
First your English is far better than my French and thanks for being able to read my questionable English.
As a dive customer I understand your point of view however I do believe your expectations are not realistic. As a manufacturer and a Shearwater (SW) customer I will say that SW goes well over and above with their customer service. I have fortunately had years of reliable performance with both of my SWs without a single issue. I have however had many discussions with them regarding possible improvements and they have always been responsive and open to customer input, I'm sure that they are listening to you through this thread, though your concerns IMHO should have been privately communicated with them on this particular matter.
As others have stated you choose to go directly to the manufacturer, if you had first contacted the dealer you likely would have had your unit swapped out and the dealer would have resolved the problem with SW. What you need to understand is that when a manufacturer uses a dealer/distribution network the price to the dealer/distributor is considerably less as the dealer/distributor takes on partial responsibility in order to make a profit. When you go directly back to the manufacturer it is not reasonable to expect the manufacturer to pick up all of the shipping and other costs.
From experience I can tell you that not all customers play fair. A small amount of people will do all they can to take advantage which forces us manufacturers to protect ourselves from very real fraud. They are doing everything they can, to provide excellent customer service, while not going broke. When a package is "lost by the shipper" it is a red flag for possible fraud. I understand that this is not your case however try to understand the situation from SW's perspective. UPS is a big company and they move a lot of packages every day. When something goes missing or is outside it's delivery window it can take a few days for UPS to sort it out and get back to the shipper. During that time SW is wondering if they have that rare occasion when someone is trying to take advantage of them. Remember they don't know you.
No matter how good a manufacturer is and no matter how much quality control a company does there will be units that fail out of the box in the field. SW has an excellent reputation for their products, warranty, & customer service. I have a dive buddy that is very abusive on gear and does some extreme dives that has cost SW a good bit of money because they stand behind their product so well. Things happen and most of the manufacturers do everything they can to provide good or better customer customer service. We are people on the other end of the line and we don't have all the answers however most of us make our best effort.
The last thing to know, as others have stated, that days in the business world are normal work week days, weekends and holidays are not counted. I just had a customer that had a problem with one of our products. They are on a dive trip and needed a replacement to get through the trip. I know this customer and had no issues shipping a loaner to get them through the trip however I have zero control over the holiday day that we had this week, which the customer understood.