Sleight Build (Racial ability)

After thinking about the Powerful Build ability for a while, I got to wondering why there wasn't one that went the other way. So, I came up with this!

Sleight Build
You are very slim and light for your kind, and can get places they would normally be too big for.
Benefit: You are treated as one size category smaller than you actually are whenever being smaller would provide a bonus. A medium-sized creature with this ability is treated as small size for their Hide and Move Silently bonuses, attack rolls, and AC, but does not have the reduced carrying capacity, their weapons are not reduced, and they do not take the -4 size penalty that Small creatures normally take on grapple checks.
Special: A creature with Sleight Build cannot benefit from any effect that would provide the Powerful Build ability, nor can anyone who possesses Powerful Build benefit from Sleight Build. If someone with one ability would gain the other, they only use the one they already possessed.

One kinda already exists: Kobold web enhancement

Slight Build: The physical stature of kobolds lets them function in many ways as if they were one size category smaller. Whenever a kobold is subject to a size modifier or special size modifier for an opposed check (such as Hide), the kobold is treated as one size smaller if doing so is advantageous to the character. A kobold is also considered to be one size smaller when "squeezing" through a restrictive space. A kobold can use weapons designed for a creature one size smaller without penalty. However, the space and reach of a kobold remain those of a creature of their actual size. The benefits of this racial trait stack with the effects of powers, abilities, and spells that change the subject's size category.

Click to expand...

I don't much see the point of this, really....it's all benefit with no drawback, and it's a couple of feats' worth of benefit (+1 AC all the time, +1 on all attacks, +4 Hide). Powerful Build itself is annoying like that too, but at least makes more sense for a Medium race, since there's a significant variance in Medium size, so it's more plausible for a race to be so close to both that they count as something inbetween.

I don't see how being really thin would make a tall, Medium-sized creature (tall enough to count as Medium size and wield Medium size weapons easily, despite being thin) would really help them dodge or hide behind most stuff (aside from trees). They're too tall to easily crouch behind stuff, and too tall to just duck under an ogre's club swing or whatever, etc. Nor do I see how being really broad and blocky, while being some 3 or 4 feet tall, would make a character harder to hit than a human or easier to hide.

But there's a more significant difference between Medium and Large sizes in terms of height, build, and bulk. Though I still dislike the all-beneficial nature of Powerful Build.