The WL IS totally and only for the benefit of the school, and the school does not (and IMO should not) have to convey how many are on it as that is irrelevant to YOU. A WL could be 500 deep and if you are one they want and need, you’ll get off it. A WL could have only 5 and if you are not one they want or need, you won’t get off it. In either case, you have zero ability to assess chances.
Consider a WL a rejection and move on. If you happen to be one of those who get the call, you can deal with that news when it comes, but you should assume it will never come.