Is the Rokinon (Samyang) 135mm f/2 ED UMC Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 135mm f/2.0 test image. Observe the contrast and resolution of these results.
Is the Rokinon (Samyang) 135mm f/2 ED UMC Lens set to 135mm f/2.0 sharper than the Sony FE 135mm F1.8 GM Lens set to 135mm f/2.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.