If you go back and read again you will find that those values are for normally fed brine and wild brine, none of them gut loaded. Gut loading adds to those values given.
As for frozen figures, the packaging is misleading because the brine shrimp industry chose eons ago, to give values based on total packaging. In other words, the protein is a percentage of all the brine as well as the processing and packaging fluids.
Mysid shrimp on the other hand, like most other foods, give values for "dry weight" even though they are not "dry" when packaged.
When you compare "dry weight percentages" for all foods, frozen brine is still varying but around the 50% range, when no enrichment has been done.
If you were to take spirulina flake that I use for instance, and wet it in the tank, and then give the protein level as a percentage of the total, you will now be down under 10% just like frozen brine shrimp. The same applies for other dry foods.
What it boils down to then, is comparing apples to apples, not apples to oranges, which is what you do when you compare wet weight percentages to dry weight percentages. The water content is a tremendous portion of the weight and some companies were smart enough to list the dry weights, knowing many would compare those figures to wet weight numbers and be misled.