From the sounds of it, the new jobs will be pretty "complicated" compared to the ones already in the games.

Dark Knight utilising MP to tank - something other tanks don't really do (yes a paladin needs flash but MP isn't their primary concern)
Astrologian - stance dancing and combining cards (from the little information we know) you will need to be decisive and quick thinking.
Machinist - Turret placement and attachment priority.

They sound pretty intense based on how they've been described on paper, the only other "job" that's somewhat complex is the ninja and their mudras. Gating them behind the main story is a good thing, it will mean players can learn tanking basics of healer basics on "easier" classes and transfer those skills to the more complex ones.