I think you are confusing QNH and QFE.
The actual pressure at the airport located at 7700' will read 0' when QFE is selected, this is the actual pressure at the station.
Any reading of the altimeter taken are then Above Aerodrome Level (AAL).
Most airlines and companies do not fly QFE but QNH.
When flying QNH procedures, the airport altitude will be displayed on the altimeter tape when on the ground at the station. So if the airport is at 7700' then the altimeter will display 7700'. The pressure setting you are required to set to achieve this reading of 7700' is the QNH.
The QNH value is essential the value that reads 0' when at sea level in actual weather conditions.
The QNH only varies with the high or low pressure of passing weather fronts.
The QFE varies from station to station as the altitude of each station is different and there may be a correction for high or low pressure to be taken into account.
When flying QNH, all obstacles around an airfield which are referred to an elevation above sea level, are referenced to through the altimeter.
When flying QFE, all obstacles around an airfield are referred to in relation to height above/below airfield elevation. This requires continuous changes to the usable QFE when transitioning to areas away from the airport used for reference and new charts need to be referred to using a different reference station.
Airline operators predominantly use QNH. When flying higher in the sky in the airways, flight levels are used, all of which are based on all aircraft flying the same Standard setting, or 1013hPa, the worldwide acclaimed average standard pressure. This then results in all aircraft maintaining required separation.