They are still around because they made 170 of them
Which is a tiny number for an aircraft and proves my point.
The Deboost sysytem allowed for double hydraulics with wire backup saving the weight of a triple hydraulic sysytem.
It introduced the "fire Handle" concept (E-handle) where a single action secures the engine. No seperate feathering, fuel cut off, etc.
16,000 equiv Shaft Horse Power, which was double the same weight DC-6.
75% of the wing is swept by the prop airflow resulting in a huge amount of induced lift/stall supression.
Automated heating and cooling. Automated pressurisation control. Bleed air anti icing and de icing, and yes it took a huge amount of air to do the job but then there was a spare engine or two.
Easy to fly on 3 engines (just as well).
In freighter mode 2 spare generators.
Ok they were a bit tired by the time I got on them, but for the crews transitioning to them in the early 60's they must have been like space ships, speaking of which, if you go into the apollo space capsuals you will see a lot of the same switches dials and electrical systems.