It is somewhat difficult to answer that question because "importance" is not something singular, but rather different things are important to different people.
Studies of the variance in student performances suggest that while teaching is one factor that does affect student performance on standardized tests, its effects are actually only moderately significant when compared to other factors such as parental income.
Next, there is a question of what makes a great teacher. While some people evaluate a teacher's ability based on student evaluation scores, those actually correlate more strongly with gender and physical appearance (men score higher than women and younger, better looking people score higher than older or less sexually attractive people) than with anything substantial.
In my opinion, subject matter knowledge is the single most important skill a teacher can have. No matter what a teacher's pedagogical abilities, someone who teaches that the sun revolves around the earth or that the world was created 6,000 years ago or similar nonsense is doing a great disservice to students.
Democratic societies rely on having informed voters, and teaching students to think critically is important in grooming future voters, thus making teaching skills important to civic society.