Color me skeptical about prime lenses, when you can pick up a 24-70mm f2.8L zoom for the same price. If you look at the lens resolution charts on Canon's website, it appears that the 24-70 is a much better performing lens. I'm certainly not an expert but below is the 50 mm and the 24-70 at 70mm MTF chart. From what I can see, the zoom blows the prime away. Since switching to primarily zooms, the versatility of a variable focal length lens works for me.
Eh I'm guessing you don't know how these tests work, but they're often low-moderate frequency tests as well as these #s are wide open. It's a bit misleading to compare a super fast prime vs. a zoom.
When it comes to high-frequency resolution such as MTF50, especially periphery at optimum aperture, zooms are absolute garbage compared to primes.
In this case you're looking at 2.8 vs 1.2 at mid frequency. So yeah the zoom will show higher numbers.
But for ultimate detail in an absolute sense, particularly towards the mid/edges/corners, a decent prime will trash a good zoom in fine details. Go read Roger Cicala's blog at lensrentals on this.