Couple of observations about these various scales. First, they are not real scales; the distance between levels is not consistent. For instance, Level 8 in the Vail scale is still worrying about moderate terrain, while Level 9 is a "virtuoso." Level 1 is never skied, and 2 is for folks who've spent less than a day on the snow, yet Level 3 is doing consistent wedges. Not a consistent interval. Meaningless.
Second, the various charts all assume uniform achievement. I'd guess that for many here with tired knees, carving on challenging terrain is more straightforward than doing moguls with consistent speed and rhythm. Or some will really shine in powder but drop a level on ice, or vice versa. Let's face it; even some of the best skiers here prefer certain conditions or terrain and tend to avoid or shortchange others. If you think after a few decades of this you're equally good on everything there is to ski, you're deluding yourself. So if we use the least developed skill as the anchor, most here will drop a level. Or two.