You're right when speaking of S7 -hate this season! But other seasons showed characters in the lead and handling it very well. Xander in Graduation Part 2 and when Willow was out in S6, he had to take the lead and ordered Anya and Tara to head to the Magic Box. Willow was shown to be a good leader from time to time -especially after Buffy's death. Also, Giles had his leader moments in the earlier seasons.
you're right in some degree, they do show some form of good leadership, but its only in one of the 2 cases:
-Buffy isn't around to compete with their leadership.
-Buffy made the decision to make the other characters leaders in a small faction of their whole group, or maybe the leader of the whole group.
they give other characters some moments, but if that moment undermines Buffy in any way, they tune it down.
its not just about her being the better leader, but Buffy masks every other character's abilities in the show, especially her boyfriends, just compare Angel & Spike in Ats to Angel & Spike in Btvs, they were worthless fighters in Btvs, I know Buffy is stronger, but the way they show it, they're just another one of those worthless scoobies. the same goes with Faith, compare her to the Ats variant, she was shown as a real slayer, not a pumped up potential like in Btvs S7.
^^^this only covers how Buffy masks the strength of other characters, they also get more respect & better treatment in Ats. it makes me sad to blame Buffy, because I really like her.