Is the Sony FE 200-600mm F5.6-6.3 G OSS Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 600mm f/6.3 test image. Observe the contrast and resolution of these results.
Is the Sony FE 200-600mm F5.6-6.3 G OSS Lens set to 600mm f/6.3 sharper than the Nikon 200-500mm f/5.6E AF-S VR Lens set to 300mm f/16.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.