Weep holes and clamping drains are part and parcel to a conventional shower construction, and the gravity and draining on that was what was said. Except during a flood test, a shower NEVER should see pooled, liquid water on the membrane ever again (except possibly in a conventional shower's liner). The tile and grout will wick some, but because there's not a huge, thick, absorbant mudbed beneath, it dries to the surface quickly once you stop showering.
If you take some virgin Kerdi and sprinkle some water on it, it will bead up. Eventually, it will go into the fleece. Your picture does not appear to be of a shower, but some mock up and the Kerdi is not well adhered to the backing material. Initially, the water will bead up similar to a bead of water on a nicely waxed car, eventually, it will wet the surface and then the meniscus will invert. Water will wick a little into a seam, the more thinset you leave there, the further it will wick. If your seams overlap at least the minimum specified, it will not get beyond the seam into the backing material. That is the goal, and if done right will make a perfectly waterproof shower as once the tile is installed, very little water will ever get to the membrane and certainly not enough to pool long enough to do anything. That is the beauty of ANY surface membrane.
Once the fleece does get wetted, it also acts like the pad of a humdifier, and can significantly increase the amount of water lost to evaporation during any extended leak test. The small fibers significantly increase the surface area and lots more water will evaporate from that larger surface area. Just like in an evaporative cooler or a home humidifier.