I did read the whole thing and I will respectfully disagree with about 90% of it.
My first problem is... any chance you could post in a legible color? Why post something so thoughtfully written in blue on a blue background unless your goal was to be irritating? That text has to be highlighted in order to be read.
I earned my masters degree making fish food for the aquaculture industry 10 years ago. I have been in many fish feed manufacturing plants, I have been in hundreds of aquaculture facilities and I have gone to the wheat rendering plants to attain the "wheat midlings" needed. The food I made used the waste product from the local quohogging industry as the protein component, but in order to do a fair and controlled study I had to also make the same recipe using fish meal instead. I also grew control fish on Zeigler brand pellets (an aquaculture industry standard.)
The wheat grinders have huge dust trays to catch the middlings, those trays are swept out. Any on the floor under the machine is added to the pile.
I have raised fish on pellets, home made food that is made with industry ingredients (fish meal) and home made food made with quohog bellies (also industrial garbage). I do know what I am talking about.
If you want to grow healthy fish you need to use healthy ingredients. Its the difference between survive and thrive.
Yes, your fish will survive on that Purina food, no they will not thrive on it. As you said... they are just fish. So, be happy to have them survive and feed them industrial waste. That is your choice.
Anytime you want to see healthy and thriving fish, let me know.