That's how you would design a filter class, if you were trying to actually treat students fairly. The point is that de-facto "filter" or "weeder" classes can arise wholly organically (as in, 100% organic banana peels!) as the hopefully-unintended consequence of abysmal-quality teaching. And OP seems to be talking about something very much like the latter, not the former.
Yeah, I guess I'm kind of nostalgic for the days when being a college instructor was still considered a viable profession in itself.
Not that you put banana peels in front of the students (like problem sets with no exercises). As it to discourage them for the sake of discouraging them.