For that example you gave, neon tetras are super active and should never be housed in less than 10 gallons, 20 being better, 30 being best. Personally I'd have to say I wouldn't care if someone had 40 years in fish keeping or 2 years in fish keeping, were beginner or advanced, it goes along the lines of "they can survive, but can they thrive?" I know people who have had goldfish live up to 5-10 years in a bowl. Doesn't mean it was the right thing to do. If I come across as mean sorry :) I just don't want to see more stunted fish, sick fish, or stressed fish.
Also, OP what I find works best for feeding time.... is a wider feeding area... I found it more difficult for a few guppies and a betta to be together and not get on each other's nerves (or like you found with your skinny glofish who won't get food) in a smaller space, than a larger one. In a larger space, there is more room to feed. That's also why I love my long tanks