Is the Canon EF 28-135mm f/3.5-5.6 IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 35mm f/16.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 28-135mm f/3.5-5.6 IS USM Lens set to 35mm f/16.0 sharper than the Canon EF 24-70mm f/2.8L USM Lens set to 35mm f/11.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.