All of the experts support hypo. A lot of what you read on the web, may be old info. Additionally, in many situations, copper is easier. Especially for those, like professionals, that have to deal with massive outbreak.
And, let me say, while we may have a lot of respect for many professionals, most of them are by far no experts in fish diseases. There are a few who specialize specifically with fish health and diseases. Try doing a search on the web for Steven Pro and Terry Bartelme and topics on Cryptocaryon irritans.
I have never said that copper is not effective. It is, however, toxic to fish, and fish tanks and needs to treated as viable, yet toxic medication. And tangs and angels are not good candidates for copper exposure.
If you are up to it, post up those situational thread where you found problems with hypo....likely other things caused the problem with the treatment, but, I have an open mind, and it could be a learning exp if you care to post up your research you've done here.