From what I understand, they are and always will be, because the zoom needs to make certain sacrifices in order to get the zoom ability. More glass elements, less light, maybe a longer-than-absolutely-necessary tube where light can be lost.
For sharpness, zooms have a sweet spot. I think to get a zoom that is at its maximum sharpness throughout the entire zoom range, they would have to use a ton of extra glass and make it a lot heavier. So they settle for making a lens with a sweet spot, and when you're not zoomed to that exact sweet spot, you're settling for 95% of whatever sharpness the lens is capable of.
The prime is always dishing out 100% of what it's capable of, and doesn't lose that extra bit of light, so it should always be a little better.
But that's all other things being equal. A $2000 canon 100-400 zoom, while it loses to their 400mm prime, probably beats the hell out the $150 Rokinon 500mm.