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 16mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Canon EF 16-35mm f/2.8L II USM Lens set to 16mm f/2.8 sharper than the Tamron 15-30mm f/2.8 Di VC USD Lens set to 15mm f/2.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.