Not really absolute - my assessment was still relative to big mountains I've skied out west, not any true absolute. And no, marking a mountain like Whitetail as almost all blue is not real useful. It's definitely useful to a lot of skiers to know that the "double black" run is somewhat harder than the "single black" run - even if neither is all that hard.
It was definitely useful to me before when I was a much worse skier. A lot of undifferentiated blue runs would have been more difficult to navigate/understand. (Though I'm biased by having grown up skiing in the mid-A. Obviously in some places that "difficulty" such as it is, already exists - the variety of blue runs someplace like Vail or Snwomass probably encompasses the difficulty level of most of the blue and black runs in the mid-Atlantic.)
I guess to my thinking, you don't want a whole lot of colors, because that's confusing and hard to communicate. But you also don't want such broad colors that you wind up with mountains of a single color, because that's not helpful. So you wind up with what we have - 3 colors that always have the same general meaning, but with the specifics determined locally.
Whitetail is not a steep mountain. If you compare that mountain to a steep mountain out west then you might have a case. Snowmass is not a steep mountain. To say that blues there encompasses black in the mid-atlantic is purely psychological. The lower part of Exhibition is steeper than any blue at Snowmass. The pitch is somewhat equivalent if not steeper than Garrett Gulch, a black diamond at Snowmass. Many other mid-atlantic resorts have steeper runs than Whitetail. If you look at the Face at Wisp not far from D.C., it would be solidly black at Snowmass in regards to pitch. It may even be the steepest black. They use a winch to groom it. The pitches are short, but if you factor in snow conditions and mogul sizes, many blacks in the mid-Atlantic are easily comparable if not more difficult than blacks at Snowmass. Besides measuring these slopes, I've also had little kids at both these areas in a single season, and the kids were so much more competent on the blacks in general at Snowmass than the blacks in the mid-Atlantic largely because of the snow conditions. Green, blue, and black are pretty similar east and west. Double black in the mid-atlantic is just a sham. If you count them as blacks, which they should be, then blacks east and west are even more comparable. Double blacks out west are truly steeper and more difficult than anything in the mid-atlantic.
At these mid-atlantic resorts it's a common experience to get on a lift and have someone feel it's necessary to convince you that they've done real skiing out West. It's kind of like a rite of passage for someone to tell you that you really haven't experienced skiing until you've gone out west, and they can enlighten you. Having lived and skied many seasons in both areas, it got kind of old in the mid-atlantic to hear at the beginning of every conversation about skiing, "Have you skied out West?" I swear people try to preempt each other expounding on the superiority of Western skiing. Definitely, Western skiing is so much better. I'd get on a plane to ski out there, but never vice versa. Still though, with this culture, there's a mythology that's built up that goes beyond reason. The relative difficulty of green, blue, and black slopes is one of them.