>>38491356It seems like given their portrayal the Gym Leaders are intended to be sort of like stand out members of the cities and towns they live in, so they're well-known and usually respected in some manner helping out with other functions of the city/town outside of being the Gym Leader. The Elite Four strike me more as simply the strongest people of the region and more so can be trainers who had after years of training been contacted by the League Officials and offered the position of Elite Four when one of the older members was planning to retire. My guess is that every Elite Four member had at one stage or another prior to becoming a member defeated a champion in that region and kept in contact with the league officials.
Since the Gym Leaders need to be stand out members of their community one using Dark-Type Pokemon which are notorious for their nefarious tactics and behaviour would likely be heavily contested as a gym leader if not outright ousted. It would be interesting to see that sort of dynamic but I think that's why we don't see Dark-Type Gym Leaders and even if we did they'd be exceptionally rare.
