And their leadership styles are polar opposites. In Excalibur, Kurt thought before he acted, he didn't take unnecessary risks (but he did take necessary ones, like when he threw Rachel into the mouth of an energy-draining creature about to eat them in Excalibur #16, causing it to be destroyed from power overload), he paid great heed to the well-being of his teammates, soothing the conflicts and fusing them together as a team. The conflict with Brian could very well have torn the team apart, had Kurt acted like most people would. But he didn't. He also showed great self-awareness and ability to adapt.All the leadership stuff... Rogue is leading the X-Men now and I've always thought she was dumb as a bag of hammers.
Rogue takes huge risks. That's her thing - that she's unpredictable. Sometimes, that comes in handy, but I wouldn't call it a very good leadership trait, overall. And as we can see in X-men right now, it's all coming back to bite her in the buns. It's an entertaining style, for sure, but not very practical.
So while having a leadership role in itself isn't proof of intelligence, how you handle it is. And Kurt handled his very well.