Her intuition about the finer grind is correct. If you grind the beans too fine, as for espresso, or not even that fine, yes, you'll have a not so clear cup, with some fine deposits at the bottom.  These filters work best for filter/pour-over, which will usually be ground coarser. In my 11 step grinder, where the finest espresso grind is 1, I set it at  6-6.5 for best flavor and cleanest cup.

However, as you already noticed, stainless steel filters have a superfine mesh in them, which is the actual filter. It's not like a simple perforated colander. So there isn't a real difference in steeping time and extraction with paper filters, and the residues that make it through are really really fine and can even be drunk without problem if you want.

As for the Japanese brands -- they just do everything better!