Don't know if it's just me, but I find talk of what quantifies "twitchy handling" to be very much determined by the individual and what they personally find twitchy or stable. Have seen first hand when switching bikes with friends that some people are just not comfortable with a given bikes handling characteristics and can find it nervous, where it perfectly fine for someone else.
Perception comes into it I'd say, just as being comfortable at speed, as shown in some of the answers here concerning what different individuals feel as a comfort level at a given speed.