Is the Canon EF 100-400mm f/4.5-5.6L IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 800mm f/11.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 100-400mm f/4.5-5.6L IS USM Lens set to 800mm f/11.0 sharper than the Sigma 150-500mm f/5-6.3 DG OS HSM Lens set to 1000mm f/16.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.