Well ya it does correlate to difficulty, mental difficulty. If you spent the time riding somewhere, you will be kinda mentally fatigued when you do the fight, thus being less effective during the fight.

Also the faster you can travel places the faster you can get stuff, thus making it easier to get better stuff, thus making the game easier because you had to spend x time getting somewhere. If we didn't have teleports or what have you, non of you would have all classes 50.

What? LoL Who the hell gets mental fatigue from riding a chocobo, or waiting on airships? Seriously, this is the most outlandish statement I have seen in this thread so far. As for leveling fast, you honestly think that one had to travel far to level? If someone wants to level a job fast, they don't need to even leave a zone. It's utterly ignorant to think that not having teleports would somehow prevent anyone from having all 50's with the current leveling format.