I think part of the misunderstanding going on here is that a QT tank is thought of as an inferior environment. The QT tank should be a superior environment to the main tank, because the fish will not experience any stress from bullying or competition for food.
In the short run the most important thing is getting your fish eating and building up its immune system and general health. IMO this is usually best accomplished in a quarantine tank. There are only a very few fish I would not quarantine--mandarins, some wrassses, and some anthias.
