Is WoL the only one able to master/handle all the classes at once?

[RyuDragnier]

I always chalked up the WoL's ability to easily pick up new disciplines as a manifestation of their Echo. Just like their uncanny knack for finding things that give other people trouble.

Considering what we know of Shadowbringers...

It could have also been something they had the power to do way back in Amaurot as the 14th Member of the Convocation.