Is the Canon EF 70-200mm f/4L IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 200mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 70-200mm f/4L IS USM Lens set to 200mm f/8.0 sharper than the Sigma 35mm f/1.4 DG HSM Art Lens set to 35mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.