The airspeed & other mechanical indicators are not the primary indicators.
These steam gauges are secondary to the big MFD display and that is largely driven by GPS input
The steam gages might be secondary to the HUD or the glass displays in the cockpit, but the pitot static system is vital to controlled flight. The flight control computers get their airspeed information from the pitot system. GPS can only tell the pilot groundspeed, not airspeed.
There are three instruments that are vital to maintaing controlled flight in the clag: airspeed, altimeter and VSI (vertical speed indicator). All three are driven by the pitot static system. It fails in the goo and the aircraft crashes.
“that is largely driven by GPS input”
Indicated Airspeed in never derived from GPS position data. Indicated Airspeed must be driven by measured air over the wings.