As a worship leader for over 20 years, I've experienced that the majority of worship leaders and church musicians fall very short in the area of music theory. Many know just enough about music and their instrument to fill a spot on the team, and sadly most of them have zero motivation to be anything more than what they are today. Of course, it's not a sin to lack a solid understanding of music theory. However, it's not right to just hack through... to just "get the job done", etc.