Is disc-braked equipped bike more susceptible to theft?
My title pretty much says it.
Susceptible means facilitating or easier.
Disc brake bikes are not more susceptible or easy to steal than a bike with rim brakes.
They are usually more attractive and get more attention.
(IF you saw this before the Edit, the XR-200 is not a good comparison to my Sorrento)
They're more expensive and flashier so thusly more attractive to a thief
That doesn't mean I wouldn't put discs on my bike though, just lock it up well
Not enough to worry about if you lock up your bike properly. Thieves look for bikes that are easy to steal. They usually aren't selling them to bike fanatics, but rather a fence who will pass them on, so the type and quality of the bike makes only a small difference to the sum the thief receives.
The bottom line is that bikes with cheap locks or bikes that are improperly locked get stolen the most.