It is a common Christian error to believe that a person with a big ministry is automatically Godlier than a person with a small ministry. While it might be true, it doesn't have to be so. God is working out a plan to redeem His creation, and He uses people to carry out His plan. Saul was actually chosen as king because God's people had rejected God's plan, wanting a kingdom instead of being ruled by judges.
When God's plan calls for a large ministry in a certain geographical area, it doesn't prove that the Christians involved are spiritual giants. They might be, or they might have gifts and abilities that fit into God's plan. Your job, as a Christian, is to grow in grace and knowledge, and then to submit to whatever God tells you to do. If you do that, you are a spiritual success, regardless of what God calls you to do.
King Saul failed to acknowledge that God had called David to replace him. He might actually have discerned sins in David that would cause problems later, But his refusal to accept God's will for his own life produced the jealousy that eventually destroyed him.