Is the Canon RF 14-35mm F4 L IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 20mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Canon RF 14-35mm F4 L IS USM Lens set to 20mm f/5.6 sharper than the Tamron 17-35mm f/2.8-4 Di OSD Lens set to 20mm f/16.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.