There is a difference; you can fight off these conquerors and survive.
The points Vit20141012 mentioned are rather ridiculous. His first point relies on Mongolia doing almost exactly the same thing every game, even prior to 1237; they must be in the same location, must have amassed an army, must have survived, must not be threatened (I mean, if they're collapsing or being invaded, starting a war with Russia is nonsensical), and ever so on. It's actually quite heavily scripted already, I believe, but it's a good balance between freedom and history. Point two already exists, in that Mongolia is likelier to raze cities.
Points three and four rely on this again; all the European countries must be alive, they must have the same alliance structure as in our world, they must roughly control the same territories, they must roughly have the same power, and ever so on... As a European country, your role would be to continuously click 'next turn'; you couldn't do anything else, because otherwise, points three and four wouldn't happen.
What if Rome survives and beats France? Impossible, if Vit20141012's ideas were implemented, for France is needed for the Napoleonic War. What if France has a defensive pact with Prussia / Germany? Impossible, because of WWI and WWII. What if the HRE conquers France? Impossible. What if France conquers Spain? Impossible. And ever so on. Vit20141012's ideas would make this mod rather terrible.
Basically, Vit20141012 says 'script this'. Leoreth says 'provided this happens, that will likely happen and we will make this likelier through scripts'. Leoreth's attitude gives freedom, fun, and history. Each game can be completely different - yet roughly historical as well. Vit20141012's attitude would essentially create a video of world maps through the ages, where you can only keep clicking 'next' to see the next year. A bit exaggerated, maybe, but still.