Is the Zeiss 21mm f/2.8 Classic Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 21mm f/4.0 test image. Observe the contrast and resolution of these results.
Is the Zeiss 21mm f/2.8 Classic Lens set to 21mm f/4.0 sharper than the Canon TS-E 24mm f/3.5L II Tilt-Shift Lens set to 24mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.