Yes, You are very right. Nothing really matches good QT. I am not the best at it. I strangely have had more luck moving fish that have become sick (sometimes VERY serious) to my QT than bringing in new fish for preventative treatment.
But anyways. I agree with you completely. Doing it right is super important and water quality is a very important element in good QT.
I like Methylene blue because it can be a preventative, as well as help with fish that have broken out with a bacterial/fungal issue.
It also helps with poisoning (Ammonia or even Cyanide).
The main thing I've noticed with Gobys, Blennys, and Dragonetts is that they often are skinny and stay skinny despite large amounts of food, vitamins, etc. and don't seem to have internal parasites.
This is purely anecdotal, but I am willing to bet it has to be poisoning related. Whether it is from too much copper from distributors/wholesalers, ammonia poisoning when in transit, or how some fish are caught with Cyanide.