F3S
I've seen screen that did not compensate for QNH difference.
If altimeter readings would be transmitted, you would see me jump up and down as I change the altimeter. QFE fields like Sofia (LBSF, elev. 1700'+) come to mind immediately. You'd see a mulititude of RA in stack if someone spu nthe baro knob.
How yould you feel about providing separation to someone with incorrectly set altimeter???
No way. Mode A is strictly QNE information and this provides for some major benefits. It is alco ATCO's responsibility to ensure terrain clearance under radar vectors, right?