I'd say your right in retrospect, solid QT protocols are key.
Some prefer to QT and observe everything, some (myself) will do preventitive hyposalinity treatment on new fish.
It's a good idea to also QT anything wet (any coral, invert, rock exct) just in case.
FWIW, from where your at now, I'd suggest finisihing the copper treatment (check that level every day if not twice daily), but also not returning any fish to the display for 6-8 weeks min. This time will allow any remaining ick cysts to hatch out and die off in the dispaly. If you do a 2 week copper treatment then put the fish back, the display will likely still be infected and the fish could get sick again.
On your losses, that's a big bummer. IMO it was probably the stress of being caught, poor water quality in the QT (hard to avoid unless you have it set up and cycled in advance), and or the ick being very advanced by the time treatment started. Also, just to cover the bases, I'd suggest reading up on marine "velvet" as well. It doesn't sound like that was the problem, but if it was it would explain very rapid deaths.
Unfortunately ick is very common, and it often lives in our tanks at low levels of infection for a long time until some stressor causes it to show up with a vengance. In the end there are two kinds of reefkeepers, those who always have ick in their systems, and those who are absolutely obsessive about QT and go to great lengths to keep the parisite out of their systems. (I'm not saying either is wrong). Ick is either eradicated, or managed. Both are valid approaches.
Sorry for your losses.