I too have strong views on this one ...
Here are three posts:
@larryferlazzo wrote How much "Content" knowledge do you really need to be an effective teacher?
This post stirred up a reply from @shhartley entitled content and pedagogy
Coming from a slightly different context but still relevant position, Silvia Tolisano @langwitches wrote It's not about the Tools. It's about the Skills.
My view and speaking as a high-school teacher of French, German and Italian:
Being a content expert for teaching subjects is pivotal to effective teaching. The capacity to be able to effectively teach subject syllabus outcomes based on students will "learn to and learn about" underpins quality teaching practice.