Sounds like a combination of issues is at work. One, a 559 has a relatively high seat, little recline, and front weight bias. Two, you aren't used to the stopping power of discs. Three you must have some damn grippy tires. Four, if you have to panic stop the battle has already been lost. A superior pilot uses his superior judgement to keep him from needing to use his superior skills. A newbie is not yet a superior pilot.

With my QNT with a laidback hardshell seat, drum brakes, and not so grippy but fast F-lite tires, it's impossible for my rear wheel to become airborne. My front tires skid before that happens, even on steep downhills.

I assume there is no rear braking involved, correct? Cuz aggressive rear braking will crash you quite readily.