The real purpose of a QT isn't to treat a fish it's to give the fish sometime to settle in before you move it into the MT, get it use to eating the prepared food that you will be feeding it, and most important study it to see if it has some sort of parasite or disease, and if it does, start to treat it with the correct medication.
Hypo is good but it doesn't kill velvet or gill flukes. Same thing with the transfer method. Copper will kill Ich and Velvet but not gill flukes or other things, and you need to make sure that you're treating at the correct levels otherwise it doesn't work.