That opinion mostly holds true to pure brine, or live brine that are more than 24 hours old. The best brine to use are juveniles which still hold their egg sack.
Most products on the market are gut loaded, or otherwise soaked in various forms of vitamins or fat. Most products also have a "guaranteed nutritional value". So they at least have X amount of protein, fat, fiber, and so on.
A quick comparison between almost any frozen brand of brine vs mysis, you will find the mysis usually has twice the nutritional value as brine.
That said, variety is key. Spinach is good for you unless its all you eat every day.
While i do not have a link to raw data, a little google digging should yield the results your looking for. If you do find anything, post it here!