In 2001, Tanaka stated he was inspired by Everquest and used Final Fantasy III (or V) as a base for the world, so yeah, it is a clone, but it's a 
Final Fantasy based clone, which is why when XIV rolled around, people reference XI because realistically, comparing the two, they should have left XIV as 'Rapture', since the namesake of Final Fantasy generally makes people expect certain things to be in line, which 
Final Fantasy XI did a 
good job at bringing in a lot of Final Fantasy aspects.
Much like when I played World of 
Warcraft, I expected quite a bit of Warcraft lore and feeling.