I think locking access to new Jobs is a HUGE mistake..

[Adire]

Also going back to the mass craze that was Ninja levelling. DF times on my server were abysmal and selecting all languages made no change to the times what so ever because vast majority of players were levelling NIN. Imagine what it would be like if newer players could all level Dark Knight/Machinist/Atrologion on day one of expansion….

DF was like this due to the fact that NIN was the only class released at that time. People who normally played tanks and healers most likely were queuing as dps.

With Heavensward, we have a new class for each role to please people who prefer each role. I doubt it will be a repeat of the NIN chaos, or would be even if newer players could use those classes. Seems like it would really keep things as balanced as always, though you'd be seeing parties made of up a Dark Knight tank, an Astrologian healer, and 2 Mechanists more often than not.