The classic approach is to have three sensors, so in case one fails you can know which one. Having two only indicates something is wrong but is not useful on the fly.
Air France 447 [1] three independent air data systems, two of them failed due to environmental conditions
XL Airways 888T [2] three independent AOA sensors, two failed because the plane was washed without the right covers in place
US Airways 1549 [3] two independent engines, both disabled by bird strike at the same time (No fatalities)
Qantas Flight 72 [4] three independent inertial reference units, bug in voting system if a single sensor's output had multiple spikes 1.2 seconds apart (no fatalities)
An in the data centre, no amount of power-supply redundancy will save you if a technician pulls out the power cables on the wrong server :)
[1] https://en.wikipedia.org/wiki/Air_France_Flight_447#cite_ref... [2] https://en.wikipedia.org/wiki/XL_Airways_Germany_Flight_888T [3] https://en.wikipedia.org/wiki/US_Airways_Flight_1549 [4] https://en.wikipedia.org/wiki/Qantas_Flight_72
If true, it's possible signal averaging isnt necessarily the best choice
Which can also fail:
In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board.
The same problem arose again on a 2014 Airbus A321 Lufthansa flight leaving Spain. Eight minutes after takeoff, two of the angle-of-attack sensors froze at the same pitch. This time, after a drop in altitude, the pilots were able to regain control and complete the flight. [1]
I don't think the fundamental problem with MCAS was the number of sensors, but that it was too difficult for the pilots to override MCAS when it faulted.
1. https://www.seattletimes.com/business/boeing-aerospace/a-lac...
Besides, those AoA sensors are EXTREMELY reliable. So reliable that some have raised the hypothesis that the real problem is not in the sensors themselves, but in some piece of hardware or software between them and the flight computers.
It seems plausible to me since failures in those sensors are too rare in the other planes but, despite that, they allegedly failed in two 737 Max 8s and in a really short timespan.