Is the Tamron 70-210mm f/4 Di VC USD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 420mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Tamron 70-210mm f/4 Di VC USD Lens set to 420mm f/8.0 sharper than the Nikon 70-200mm f/4G AF-S VR Nikkor Lens set to 85mm f/4.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.