Is the Sigma 100-400mm f/5-6.3 DG OS HSM C Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 200mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Sigma 100-400mm f/5-6.3 DG OS HSM C Lens set to 200mm f/5.6 sharper than the Sony FE 100-400mm F4.5-5.6 GM OSS Lens set to mm f/? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.