Quote Originally Posted by Alberel View Post
I think the implication is that everyone can change their class/job at will whenever they like, but the WoL is able to learn at a massively enhanced rate due to their affinity with the various soul crystals they possess. Chalk this up to the Echo; it gives us the ability to learn from the memories stored in soul crystals really easily.

For other characters learning a class/job is like a lifetime investment so very few ever branch out to more than one or two.

TL;DR The Warrior of Light is special!
This is how I always interpreted it as well.

And to be fair, there are many Echo users and (apparently) various type of Echo users.
I have always assumed that it wasn't exclusive to the WoL but to anyone with an Echo if they put their mind to learning new disciplines.
Though I'm not sure there's any evidence of that quite yet. The true nature of the Echo remains shrouded in mystery.