Imo, there's an implicit assumption that a varied diet will be suitable simply because it's varied.
I've always found the logic behind that to be rather odd, and at times over the years rather entertaining. Most of the food fights that have taken place here and elsewhere over the years have been largely based on ignorance, and rarely science.
I'll be totally honest. I think the varied diet is bs. A quality pellet is all you need.
There's the rub, a high quality nutrient dense pellet IS a varied diet.
Krill, Squid, Fish, Spirulina, Chlorella, Kelp, Red Seaweed, etc. Fish Oil, Astaxanthin, Capsanthin, Zeaxanthin, Vitamins & Trace Minerals ......
Nutrient wise, is there something missing?
I've been asking that question for a LOT of years, and so far no one has been able to answer it. At least not intelligently. If you want to think outside the box, stop attaching some weird anthropomorphic feelings to your fish as though they are little people, they aren't. I have raised many a healthy thriving fish that without a shred of doubt ate better than they ever would have in the wild, on a single pellet formula. If they were missing anything, they were too small in brain to grasp the concept. I personally believe that a hungry fish is a healthy fish, so keep them on the hungry side and trust me they will never act
bored when the food containers come out. My fish would most likely eat dried rabbit turds if I tossed them in. Go visit a commercial trout pond, catfish pond, African cichlid pond, whatever - the fish annihilate the food, and they don't get to pick dinner from a menu.
Having said that, I certainly understand that some fish cannot be pellet trained, and require fresh/frozen with vitamin supplementation - I have gone that route with certain species as well. I also feed more than one pellet formula now as the manufacturer makes too many good ones now to choose, just one.
Feeding multiple brands, or multiple foods is not wrong, nor is it necessarily better, than feeding a single foodstuff exclusively. It's all about nutrient balance, and choosing premium raw ingredients and nutrient dense foods over mediocre. 100 mediocre foods could provide less optimum nutrition, than a single high quality food.