As is, I grind in a grand total of four zones for 1-99, 6-8hrs depending on ROV KIs, as low as 5hrs w/ exp campaign + rings + 6x ROV KIs. XD
There is no balance when it comes to leveling up already.. I don't think it'd be that big a deal to let players level 2nd+ jobs using coalition assignments rather than mindlessly slaughter everything that moves in Escha-Zi'tah, or stand around and have someone else slaughter clvl mobs for you, etc.
Unless imprimaturs were reduced below 4hrs per charge, I don't see any way for it to be more efficient to level via assignments than just going out and making monsters dead. :x