Is the Canon EF-S 18-135mm f/3.5-5.6 IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 135mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Canon EF-S 18-135mm f/3.5-5.6 IS USM Lens set to 135mm f/5.6 sharper than the Canon EF-S 55-250mm f/4-5.6 IS STM Lens set to 250mm f/6.3? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.