Comparing A Natural habitat to the tank isn't logical if you don't do biotope.
Using fish tank = New Home for Fishes
While Fish Staying at 1 place they adapting.
Inside Tank, they have a limited way to go and Fish do remember tank size. Tankmates, and even every single hardscape placement.
Unlike in Nature Habitat. If they stay too long in Wild Habitat they adapting to where they used to be. And yet most aquarium fish is from breeding or even import. Not A fresh catch from the wild. So most of the fish already used to "fish tank" or maybe they didn't even know about the wild since they live inside fish tank their entire life. And there are many people keeping neon and Danios together. It's not a unique combination.
For feeding, I use some trick by using "bait". Since danios stay on top of the aquarium and neon only going to the top when there's food.
Use a small amount of food and make the neon going to the top and when both danios & Neon at the top, spread the food on your aquarium.
I can't indicate " happy fish" but I believe no stress sign is enough.
But idk. I'll let people choose. I don't really push people to believe on me that neon & Danios are compatible lol. I saw group of zebra danios killing Group of Neon bc of lack of tank space.
Just speaking out my opinion