Is the Sigma 14-24mm f/2.8 DG DN Art Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 20mm f/3.2 test image. Observe the contrast and resolution of these results.
Is the Sigma 14-24mm f/2.8 DG DN Art Lens set to 20mm f/3.2 sharper than the Sony FE 16-35mm F2.8 GM II Lens set to 20mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.