For the sheer sake of mentioning it, all caps are generally considered rude, since it's suppose to represent yelling. D=
Now then, on to the actual point, no, it doesn't mean it's useless. What it does mean is that anyone intelligent enough with a SinX will know that there are endless ways to by-pass it. SinX's SB is an irritating attack to counter. If you're in PVP, without assistance, there's a simple strategy that still works pretty well.
Simply have fury and your five spirit spheres ready. Whenever he comes close, use blade stop. Catch them, then Asura them. Most SinX will go down.