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/4.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 16-35mm f/2.8L II USM Lens set to 16mm f/4.0 sharper than the Rokinon (Samyang) 14mm f/2.8 IF ED UMC Lens (Orig) set to 14mm f/8.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.