I feed pellets daily (gasp) and the main ingredient is krill (gasp). Been following that feeding regime on all my fish for many years. This is the same manner in which commercial aquaculture feed fish, apparently it seems to work rather well. The variety is gleaned from the variety of raw ingredients that make up the food. A high quality feed will be made up of a proper nutritional balance of high quality raw ingredients.
And of course the fish I keep aren't obligatory predators, and tend to eat anything that I toss in to the tank. Not all fish are so easy to feed.
Feeding too much FD krill can be an issue due to the chitin and fluoride content. This is where variety (of raw ingredients) and nutrient balance come into play. It's not just about protein content.
Was searching about krill containing fluoride and happened to see your post. Is there no fluoride in the pellets as well?