Is the Canon EF 16-35mm f/2.8L II USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 35mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 16-35mm f/2.8L II USM Lens set to 35mm f/8.0 sharper than the Canon EF 70-300mm f/4-5.6 IS USM Lens set to 135mm f/5.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.