Speculating, since I've never seen @Xue Sheng's weapons.I am curious what kind of jian you have, and why you feel it would never be able to hold an edge? If it was properly heat treated then it should hold an edge. If it has a blunt edge, then a sharp edge can be put on it.
"[P]roperly heat treated" doesn't tell you much (if anything) about edge holding ability. Because proper heat treating depends in large part on intended function. If the blade was never intended to be sharpened, then it is entirely possible that the materials and/or heat treating would reflect that. Even if the materials would otherwise be suitable for a sharpened blade, a significantly softer heat treatment might well be chosen to decrease brittleness.