I have about 1500 hours in a Metroliner with steam gauges and no autopilot, hand flying through all kinds of weather, shooting approaches to minimums, missed approaches, all that. The non-flying pilot helps the workload with checklists and calling out "runway in sight", but it's demanding flying nonetheless. Boy did I have a good scan in those days!
I have several thousand hours in glass cockpits with autopilots. Same kind of wx and also with a copilot. I remember when some of us from our initial training class were upgrading to Captain in the Metros - the guys that had been FO's in the Saabs had a
much harder time passing the upgrade in the Metros, because they were used to glass and autopilots. When I upgraded to the Brasilia with glass and an autopilot, I remember had the most trouble managing the autopilot. In some ways at first it actually seemed to add to my workload - it just seemed easier to scan and fly - it was what I was used to.
Once I got used to it, I liked the glass a lot better, there was more information available and better organized, but I also liked knowing that I could handfly the plane if I had to, and many times I would do just that to keep my chops up. I also had my two PFD's fail on me during my IOE on the Brasilia. Nice expensive Honeywell stuff I think it was. And we trained every 6 months for multiple failures in the sim. Glass can fail in so many more ways than steam. If you've got all that nice stuff, you better know exactly what you are going to do if it fails in bad weather, and practice that regularly. I flew almost 100 hours/month in those days.
I have about 1200 hours flying Pitts and Extras X-country with nothing more than a compass, handheld GPS, airspeed, altimeter, and engine gauges. That's the safest way to fly VFR, in my opinion. You know you don't have weather capability, so you are cautious about bad wx and don't push it. You don't fly at night. Your head is outside the cockpit most of the time, because there is just not much to look at inside! I think having more stuff in the plane has a very real danger of making the pilot more complacent, and more willing to fly in dubious conditions.
Safety in flying is all about managing risk. That's why the results of the study don't surprise me. I feel like I have a fair amount of experience flying with glass, without it, and with minimal equipment. I have experience with the strengths and limitations of each. Ultimately, it does come down to the man in the box, and knowing exactly what you and the aircraft are really capable of, and not ever getting (as my first instructor used to say all the time) "fat, dumb, and happy".