The difference is exactly that - one is a fringe, tribal, nearly medieval force, the other is civilised country in the middle of modern world. If Ottoman empire emerged from dark times to become a modern 20th century society of scientists, philosophers and poets and then design methodical way of industrially murder tens of millions of people in a very short time - I'm sure we would now use "grammar ottie" instead of "grammar nazi" as a pejorative term. Meanwhile, though, they were what they were, and to most of the observers, whether Ottoman Empire were there or not, didn't make a massive difference to the volatility of the region. In short - it's not like the entire world east to west had to gather together to knock them the ef down, like it was the case with the Reich, so with all due respect to Ottoman killing force and their prospective body count, I'm afraid to say - as far as the "worst guys in history" competition goes - Nazi Germany still holds their own.