This is probably because Vultures can easily be blocked. A Falcon, which also has 16 targets, empirically tested as about equal to a Rook. Th Vulture has 4 paths rather than 3, but each path can be blocked in 3 places rather than 2. The 4 non-capturing leaps add comparatively little.
The value estimate of the Diagram takes this into account by measuring the average number of moves in randomly generated positions where 25% of the squares are occupied.
This is probably because Vultures can easily be blocked. A Falcon, which also has 16 targets, empirically tested as about equal to a Rook. Th Vulture has 4 paths rather than 3, but each path can be blocked in 3 places rather than 2. The 4 non-capturing leaps add comparatively little.
The value estimate of the Diagram takes this into account by measuring the average number of moves in randomly generated positions where 25% of the squares are occupied.