The Canon 1.8 is actually a pretty sharp lens to begin with. It has its problems, but past f/2.8 or so, sharpness is not one of them. There are of course sharper lenses out there, but all the ones I can think of are far more expensive, far larger, or both.
In this range, a more natural competitor would be the Canon 40 STM. It's very sharp, and so light and tiny that it feels like nothing more than a lens cap on a 6D. And it costs almost nothing. The only negatives are that it's relatively slow ( f/2.8 ), only manually focuses when the camera is turned on, and has zero snob appeal.