The CYA is not slow to dissolve because it is getting anywhere near saturation. It is slow to dissolve because of the amount of energy it takes for water to dislodge a CYA molecule from its crystal structure (analogous to an activation energy for chemical reactions). The rate of dissolving is going to have a far greater dependence on the surface area of the granules and on the circulation of water around them. If the CYA were more finely crushed, it would dissolve more quickly, though might be so light that it wouldn't readily break the surface tension of water and might float on top. We see this for some finely powdered boric acid, for example.
I have always added CYA into a T-shirt in my skimmer with the pump running and it visibly dissolves completely within 24 hours and I usually measure at least 80% of the expected CYA level the next day meaning that it has mostly chemically dissolved as well. Note that if I had put it in the skimmer without the T-shirt, it would take much longer to dissolve since the water velocity through the filter is very, very slow. When my pump is at 48 GPM, the skimmer might be at 15 GPM with a water velocity over it's 6" diameter of 0.17 feet per second or 2 inches per second. My 340 square foot cartridge filter only has an average water velocity through it of 0.0038 inches per second (0.1 millimeter per second) so you can understand why it takes so long for CYA to dissolve in filters.
