Is the Canon EF 70-200mm f/4L USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 100mm f/4.5 test image. Observe the contrast and resolution of these results.
Is the Canon EF 70-200mm f/4L USM Lens set to 100mm f/4.5 sharper than the Tamron 70-200mm f/2.8 Di LD (IF) Macro Lens set to 200mm f/8.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.