<p>The usefulness of a good graduate department in your major is not so much the teaching quality, but the availability of more advanced courses and research opportunities if you are advanced enough to take advantage of them.</p>
<p>Imagine if your high school had a solid college-prep curriculum, but did not have any AP, dual enrollment, etc. type of courses for more advanced students to take, or had such courses that were low quality so that students taking them needed to retake them in college anyway due to low scores on AP tests and placement tests given in college. Such a high school may be fine for many college-bound students, but those who are advanced would exhaust the offerings there. That could be analogous to an advanced undergraduate in college running out of courses in his/her major and not finding very interesting research opportunities.</p>
<p>Whether this might apply to you in your major is something you have to evaluate for yourself.</p>