Is the Tamron 70-200mm f/2.8 SP Di VC USD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 200mm f/11.0 test image. Observe the contrast and resolution of these results.
Is the Tamron 70-200mm f/2.8 SP Di VC USD Lens set to 200mm f/11.0 sharper than the Nikon 70-200mm f/4G AF-S VR Nikkor Lens set to 280mm f/11.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.