Is the Tamron 11-20mm F/2.8 Di III-A RXD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 11mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Tamron 11-20mm F/2.8 Di III-A RXD Lens set to 11mm f/2.8 sharper than the Sigma 10-18mm F2.8 DC DN Contemporary Lens set to 10mm f/2.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.