> BBC, which has no skin in the game, claims AV1 is less efficient than HEVC

The BBC does have skin in the game. They have many people in house who have invested in HEVC, and put their names behind that decision; furthermore, maybe you'll remember when the BBC spent a huge amount of money on Dirac, which seems to have continued to be extremely impractical in the medium to long term. Maybe the BBC doesn't have a spectacular track record for picking the winners in the video codec game. ;- )

Added: The BBC's comparison also seems to be between professionally-configured and tuned HEVC/VVC encoders, supported by their vendors; and what seems to be a default-configured libaom, with no consultation with the vendor.