That the cuts are proximate doesn't mean much. Skirt, from the plate, is quite thin. Brisket is much thicker. There really aren't "cuts" per se from the brisket. Brisket is brisket. One can differentiate between the flat and point perhaps - the brisket comprises two muscles - but I'm not convinced that really answers your question. In terms of flavor I don't find them all that dissimilar. But they are quite different in structure and mass. Skirt's thinness would necessitate rather low temp smoking before grilling or otherwise cooking it. Me, I'd rather just grill it with smoke wood.