IMFU,
a) I guess it depends on definition of "catastrophic"
b) Rotaries do have some areas, that need more attention than pistons - well filtered air, for an example.
c) Drone engines are notoriously failure prone. Hardly any one is made for more than 50 hrs life. That is what they are made for - cheap and expandable.
d) If you want to kill a Mazda Rotary, you will have to do something wrong. If you just slightly care for your motor (like you should anyway, piston, rotor or turbine), the Rotary will not fail in a catastrophic mode.
Accelerate a piston past its rpm range and you got a handgrenade. Push a Rotary past its redline, and nothing happens. Push it way beyond the redline and your seals might go, but it probably still runs until you shut it off.
Again Drone engines should be compared to Drone engines.
I bet that piston drone engines have a higher failure rate than rotaries...
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