Is the Canon RF-S 18-45mm F4.5-6.3 IS STM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 18mm f/5.0 test image. Observe the contrast and resolution of these results.
Is the Canon RF-S 18-45mm F4.5-6.3 IS STM Lens set to 18mm f/5.0 sharper than the Canon RF 85mm F1.2 L USM Lens set to 85mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.