Well, you do not have to agree. You found what works for you. I had a spawn of 250 (over 300 eggs initially) and I did see the stunting. Comparing them to someone else's spawn, whose fry were twice the size at the same age... It was definitely a factor. It slows growth, and has been proven time and time again. I could never do enough water changes to keep up!
If it were a spawn of... 80, then they would have grown faster. (I had two spawns going and had a good comparison).
This also shows, why it is important to find what works for YOU. My method, is probably different that Darth's. Or anyone else on here. Similarities, yes, but still different. It took me a few spawns to find what worked the best for me (shock method).
You "can" make money, but the thing is should people breed FOR money, or FOR the fish? I won't do a large spawn like that again. It took a lot of time and money.
I have also seen overpriced fish with bad finnage. I wouldn't pay that (plus shipping.. Canada sucks for shipping prices...) for a fish that maybe I know the background of, but overall the appearance looks bad. Or a fish who has a weaker immune system. I bred hardy, and I'll do it again once I have settled into my new place.
Also, on the "breed for what they want"... Ask around your area. I used kijiji to ask, and got a good number of replies. People wanted: white, red, yellow, butterfly, cambodian, giant, halfmoon, crowntail, the most. Doubletail is more unlikely to find here and way harder to breed than I even expected...