[goodcanadian]

For half a century or so aircraft height was largely done with air pressure alone.

It still is. Flight levels (20000 feet and above in the US) are defined by air pressure without reference to current atmospheric conditions (i.e. the actual altitude of FL200 can vary based on atmospheric conditions). Below 19000 feet, altimeters are calibrated to local conditions which are given to the pilots by air traffic control.

[defrost]

Still used, sure, but not solely ( 'alone' ) - it's augmented by GPS height, feedback from ground radar, onboard radar facing down and forward, etc.

See: https://en.wikipedia.org/wiki/Altimeter that list five types (including trad. air pressure type)