I wish Square would give us the option to start the new classes at level 1

[Zairava]

Palace of the dead allows you to go from level 1 again iirc

It does, but this isn't really the same idea here. You level very, very rapidly in Palace of the Dead, the OP is talking about level 1 outside of PotD. (Which more or less means they would need to level through fates or sidequests up to at least level 15 to run sastasha)