Some are much more dangerous than others. And the MU2 is a turboprop, not a piston. The MU2 has a bad reputation and the plane was recently purchased, so the Dr probably didn't have much time in it.
First, I doubt as licensed pilots with decades of experience and thousands of hours of flight time in general aviation airplanes that we have any actual disagreements. But what does a “bad reputation” in general aviation really mean to those of us who are licensed pilots? It means something completely different to those of us who are pilots than those who don't fly. To us it means that we need to pay closer attention to the factors that have caused others to have difficulties. It does not necessarily mean anything negative about the aircraft itself.
My wife frequently wants to replace our Piper Cherokee with a light twin. Most people think that twins are safer than single engine airplanes, but in fact most light twins have a higher fatality rate than than singles. As you say the MU2 is not considered a light twin but some of the same factors that result in light twins having a higher rate of fatal accidents than singles most likely contributed to this accident.
The MU-2 is a complex high performance twin aircraft that has been in production for nearly fifty years. They have logged millions of safe flying hours. The MU-2 passed all of the tests to become a certificated airplane in the United States. It has been the subject of studies and reviews by the FAA over the years and has been found to be in compliance with its original certification.
Every model of aircraft even the ones determined by decades of use and millions of hours of flight times to be the very safest have characteristics which are known to have been factors in fatal accidents. My understanding is that the most likely reason that this aircraft has been involved in more accidents is that it is an affordable complex high performance twin that any pilot with a multi-engine aircraft rating is legally allowed to fly without any additional training.
Why are Bonanzas also known as "V-Tailed Doctor Killers"? It is thought that so many doctors have had mishaps in Bonanzas because many doctors tend to be very confident in their abilities regardless of their level of training and expertise. I am certain that many times more doctors have met their maker in Bonanzas and Comanche 260s than in MU-2s. But Bonanzas and Comanche 260s are sound aircraft who just happened to be affordable by many people who probably shouldn't have been quite as confident in their own abilities as they should have been.
The vast majority of pilots live through challenging situations which came close to ending their lives. I don't know any pilot who can't give me at least one example that they have learned from. General aviation can be a very unforgiving pursuit. If the safety Nazis had their way no private citizen would be allowed to fly any small airplane; no one would be able to ride a motorcycle; no one would be allowed to ride a horse... Ultimately we would all be required to walk or ride on public transportation. There is risk in any form of transportation.