I think multiple people can have the same score.
The plane stats give you all players that had a kill or a death in any plane, gv, gun. Thus you can get all "active players" during a tour. The number went down to about 2/3rd during the last two years. Which is very much corresponding with the number of players logged in. The low point was once about 100 players (around mid day local time), now it's often below 60.
Of course, this is not meaning AH is dying, nor can you blame any single design decision or so for that. It's complex matter, and on top of that, we do know nothing about the business side of affairs.