I think using them as feeders is fine. A good reason they could be used for feeders is that because they are prolific and there is not a shortage of them. I am sure if Arowanas were not deemed the "lucky fish" and were prolific they would also be used as feeders. I think anything that comes to mind that is easily available can be used as feeders.
In the USA, the main feeder fish here in Goldfish but I have tried to source other types of feeders for my Monsters before. One of them being Rainbow trout. People could say the same about Rainbow Trout being a very beautiful fish etc etc, but it doesn't change the fact that I could get them in abundance and use them as a feeder if I wanted to.
During my search for alternative feeders, I also thought about using Large Mouth Bass Fry as feeders too. I called many fish farms about getting them but rainbow trout came out cheaper in the end. I love LMB and would love to keep a large specimen of one in my tank but I see nothing wrong with it being used as a feeder.
I think what we used for feeders is all a matter of choice. The Giant snakeheads just were easily available and so people thought "Why not?", but it doesn't mean people care less for them. I have seen many people keep them as pets in the same places were they are sold as feeders.