In my assessment, both aspects are equally important.
The Teacher's knowledge is essential for the learners' progress in terms of vocabulary and structures (any deficiencies in this respect are bound to be mercilessly revealed in any of the Cambridge exams the
ESL students all over the world so willingly take nowadays).
The Teacher's classroom methods and his/her general ability to transfer information by means of direct interpersonal communication contribute significantly to what's known as 'the student's linguistic behaviour patterns'.
The above is IMHO, of course.