then most modern airplanes don't feed any raw data to either cockpit instruments
I play with mid level turboprops these days and the fleet certainly has both raw data primary and standby flight data tucked away in amongst all the gee-whizz bells and whistles, FMSs and other like bits of kit.
Do not most (all ?) larger machines still have independent standby AH, ASI and altimeter ? It is these to which we should turn when the others start to give one the discomforts ...
The problem is that the skillset required to use them to the exclusion of the fancy stuff is quite different if these are ALL that the pilot is reasonably left with on the dark and dirty night.
However, providing that the pilot has maintained that skillset, which is becoming increasingly difficult, it is a comparatively straightforward exercise to recover the aircraft to a safe landing.
The computers are great .. but only if they are working properly.