Is the Tamron 100-400mm f/4.5-6.3 Di VC USD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 560mm f/9.0 test image. Observe the contrast and resolution of these results.
Is the Tamron 100-400mm f/4.5-6.3 Di VC USD Lens set to 560mm f/9.0 sharper than the Nikon 80-400mm f/4.5-5.6G AF-S VR Lens set to 400mm f/8.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.