The pattern is broken in Gen6, neither the Gym Leaders nor the Elite Four in XY have a Ghost specialist.
And Gen7 doesn't really have Gym Leaders in the first place, though you could also say EVERY type now has a "leader", or at the very least, a specialist.
Except Ice, for some reason (though you could make a case for Lillie being the Ice-specialist, due to her association with Alola-Vulpix).
