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 300mm f/7.1 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 300mm f/7.1 sharper than the Nikon 80-400mm f/4.5-5.6G AF-S VR Lens set to 135mm f/5.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.