Why are the frozen fillets of Cod, Swai, Salmon, and surely other meats like chicken, High Pressure Water Injected to the point where a 6oz frozen fillet of GV Cod weighed 3.5oz thawed and was so torn from the injection it had fell apart in the pan?

Many of the meats are injected. For example hamburger has a percentage of water at Walmart. You paying x amount per pound where if you went to publix and pay a few cents more you actually will have more product in the end. You get what you pay for.

There is a real problem with frozen fish. Even if it says packed at sea it's likely to be run through a machine that ensures weight to portion per package. The only regulation is for quantity not quality. Go to a fish market. In Spring Hill there's 2 good ones. Hernando beach and one on 19. Google them you will be happy you looked around.

I would go to the Publix across the street for meat

Because MONEY.