A OW Sapphire/Emerald benefit is preferred seating. Have never seen in writing what that is for each airline/class of travel/fare booking class
What is you fare booking class (not just economy)? Cash booking? Booked with AS status?
https://www.oneworld.com/travel-benefits
Access to preferred or pre-reserved seating*
*In accordance with the individual policy of the oneworld airline operating the flight.
**Priority baggage handling is not currently available on flights operated by British Airways.
Exceptions may apply.