I agree with much of what you said above.
Probably what differentiates one food from another is more about what's there that isn't needed or isn't good to eat. When it comes to predator fish, nothing could be better than the food it normally eats. It hard to argue that there could be anything in fish that is harmful or unneeded for predator fish. The nutrition profile of dried fish should very nearly be a perfect match to the nutritional needs of predator fish particularly, but possibly also for other fish as well. TP utilize plant based proteins very effectively but my hunch is that they could more efficiently metabolize dried fish.
