As far as sharpness is concerned, the 18.5mm achieves 6 out of 10MP, the Sigma 12 out of 24. How could it achieve an higher point when it resolving only 50% of the sensor pixels?
Furthermore the Canon 300 and 400mm f/2.8 score extremely low in transmission. Of course they are no f/1.4 lenses, but they are no 50mm either...What about weighting the values? A 400mm with T=3.1 should score much more than a 50mm with T=1.7, in my opinion.