I suspect the vw may not work as well with all ski combinations. For example, when I went from an A1 to a Goode, there was a signficant speed increase accross the wake. I do think the vw slows the ski down so a vw on a slower ski may not work as well.
Also remember that we want the ski to work the best at our hardest pass. For me, that is 38 and it feels dramatically faster than 35. So I need some help getting the tip to engage and slowed down in the preturn. I have skied 38 with the vw and it does help, not hurt. I don't have a problem getting width at all, my biggest problem has been dealing with the speed at the short line length. With the vw, my tip starts engaging before I can get my body in the right position. One my body gets in the right position, it makes it even better. At my opener, I can feel the ski slow down a bit too much in the turn but who cares, I want it to work at the hardest pass.
Both my wife and I had our skiing improve with vw, instantly. So there is something to it. Bottom line, the benefits outweigh the negative.