To be clear least important =/= worst of the series.

A toe in the pool? The only difference between 1 and 6's high fantasy settings is that 6 is human[-esper hybrid]s only.
I disagree. In FF6 we see the move away from a stereotypical fantasy setting into something more steam punk/industrial revolution. It didn't go all the way, but it's successor FF7 did. After that aside from the FF9 throwback the stereotypical 'medieval' setting was no longer a FF mainstay.