Leading the group is not the most important thing a group leader does.
Although that is where most churches place most of their energy in leadership training, the most important, lasting thing a group leader does is develop the apprentice leader. I've studied growing churches, different church and small group models, the life of Jesus, and the life of the early church. And they all point to this conclusion: Discipling individuals is primary; leading groups and teaching the crowds is secondary. In fact, ministry in groups and with the crowds often is part of the training experience for discipling individuals.
It goes something like this: I train you one-on-one; you watch me as I lead; you ask questions (or I ask you questions) about what I just did; you lead; I ask you questions (or you ask me questions) about what you just did; you do it yourself.
It makes good sense to make apprentice development more important. It is a way to broaden the leadership base of the church, which then increases the opportunity for more ministry and greater outreach—without placing all the burden on a few people.
If you are leading a top-quality Bible study each week, you are providing a good ministry in your group. If you are training someone else to lead, you are planting seeds for even greater things beyond your group. Jesus ministered to the crowds; he had a deeper relationship with the 12; but he spent even more time and energy with just three disciples. And those three became some of the main leaders in the early church.