Thanks, but that’s not my concern. I’m sure the TC’ers are wonderful people, and contribute wonderfully to our Catholic body, but theirs are not the concern I was addressing, which is below.
Who would be…? (If they are One of the Big Four, it would be the Superior General of their Order, only?)
And if they’re not One of the Big Four, to whom would a lay Catholic address concerns about the teaching of actual heterodoxy?
Mind you, I mysef have no current pressing interest in such a complaint!

However, I do sympathize and empathize with lay people in a position of dependency on their teachers in Catholic settings. The laity has a right to hear the truth, consistent with doctrine, from its religious representatives.
And you’re right: It has nothing to do with The Letter. However, I think it’s an important offshoot because it does pertain to the whole issue you have well elaborated on regarding structures and autonomy and lines of authority, which is an aspect of this thread.