Is the Sony FE 70-200mm F2.8 GM OSS II Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 400mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Sony FE 70-200mm F2.8 GM OSS II Lens set to 400mm f/8.0 sharper than the Sony FE 70-200mm F2.8 GM OSS Lens set to 280mm f/4.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.