Very close to right. The business model has to fit the demands of the local market.Things that can not find a nitch where they can survive will become the victim of natural selection when their protective fence fails. Local dive shop can survive but not until they change their business model. Gear needs to become a tertiary source of profit while training, service, and gas (things where the internet offers less or little competition) need to become the profit makers.
An alternative is clubs replacing local dive shops and the internet being the primary source of gear.
I don't stock gear at all. Most of my customers either bring their own gear or use rentals. For the others, I'm fortunate that my business is located at a place where there are three major wholesalers, so when my customers need gear, I take them shopping. The wholesalers give me a trade price (marked up from their own cost) and I can resell at a small markup as well to cover my time and costs. But I realize that in my case, location is everything. I wouldn't be able to do this at a place like Belize.
Training is not a money maker. Unless the industry reassesses the value of training, charging the actual cost of the training + a margin for profit rather than using it as a loss leader to get divers into the store in hopes of selling them gear, it never will be a money maker. And the divers are buying gear elsewhere anyway, so the whole loss-leader approach backfires.
In terms of other product, most shops do sell trips, but usually just a few a year. My primary source of income is in dive travel; when customers book trips, I can then try to sell training as an add-on. Gear sales comes in at a distant third. Of course taking people diving and teaching diving is what I enjoy, but the necessities of the bottom line mean that I spend at least as much time answering emails about dive travel as I spend in training divers.
Clubs may work in areas which are not dive destinations, but there's no way a club system will work on my island.