Is the Sigma 150-500mm f/5-6.3 DG OS HSM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 400mm f/7.1 test image. Observe the contrast and resolution of these results.
Is the Sigma 150-500mm f/5-6.3 DG OS HSM Lens set to 400mm f/7.1 sharper than the Canon EF 70-300mm f/4-5.6L IS USM Lens set to mm f/? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.