No, that's where you find bodyfat percentage--nowhere.

Weight is definitely in there and height is captured in frontal area. Area, as you may not know, is sometimes expressed as length (aka height) x width. Even if you think height has no bearing on frontal area, weight is clearly in the equation while BF% is clearly not. Thus, it's BMI 1, BF% 0.

Of course, W/kg will correlate with climbing ability far better than BMI which itself still has a better correlation than BF%.

All things being equal, the taller a person is, the heavier they are. It's harder to weigh 100 lbs when you're 6' vs. 5'. So you'd think taller/"bigger" people are naturally disadvantaged when cycling against gravity. But taller people generate more power which negates their inability to get as light shorter people...to a certain extent.

In order to evaluate how optimized a body is for climbing, you need some kind of ratio of height to weight--some sort of "leanness" potential or "how much more weight could I lose off of a frame of this height." This is where rules like 2 lbs per inch for a climber come in. However, it's still not a good fit, especially on the extreme ends of the range. Body mass and height don't have that linear of a relationship since body mass is really related to volume. To improve the fit you need a square or cubic function. Height/(weight^(2/3) or perhaps weight/height^2 or weight/height^3. Anything other than a linear relationship. Well, BMI is one of those formulas. Using BMI or something similar, a coach can determine how optimized an athlete's body is for climbing. Not only that but he can do so for athletes of different heights.

I feel like I'm giving away someone's trade secret here but this is one of those quiet, behind-the-scenes things that a coach does.