So "the water freezes, the alcohol does not," is not actually how freeze-distillation works. The entire batch freezes solid. You then let the block melt and collect the first meltings. If you start off with a 5% ABV solution, freeze it, and then melt off half of it, you'll end up with two halves where one is maybe 7% ABV and the other is maybe 3% ABV. You will need to reprocess those halves to further concentrate (yes, both halves, you want the alcohol from the 3% portion, too, but you have to do them separately or you're back to where you started) with your level of efficiency being limited primarily by your patience and how cold your freezer can get. Probably not cold enough to get above 20% ABV [0].

One problem with freeze-distillation is that it's more like removing watery alcohol and taking everything else than it is like in boil distillation where you're trying to remove alcoholic water and leave everything else behind. So you still need to make multiple runs to get the ABV up, but boiling will remove impurities, whereas freezing will concetrate them.

[0] IDK, that's just a guess, I'm not inclined to look it up. I'm not writing a reference guide here.