Wanted to clear up potential misconceptions:
Divisions other than e.g. the Eleventh and Thirteenth absolutely maintain presences on Earth, just that these two divisions probably have "larger" presences. Just because other divisions have specialities doesn't mean to imply they avoid the duty that defines all Shinigami altogether; rather the higher up on the food chain you are the rarer it is you "cycle out on deployment to Earth" so to speak.
The lower your rank, the "further away" from the division's duty you get and the more you become interchangeable with other divisions—remember past a certain point there can be multiples of the same seat so it's not like there are only 20 officers in every division including the captain and lieutenant.
If you're an unseated Shinigami in e.g. the Sixth odds are you work in the capacity as an MP from time to time in the same way that if you are in the First you perform clerical administrative duties once in a while but for the most part you are still just a Shinigami and you still get sent to Earth. Some divisions are probably a little more unique, such as the Fourth and Twelfth where even lower seated or unseated Shinigami are more "specialized" but the Fourth in particular deploys many of their lower ranks to Earth specifically to serve in that capacity.
So to reiterate: outside the Thirteenth where a presence on Earth is kinda their purpose (and thus all ranks are regularly there), it's common for lower seated Shinigami of all divisions to be deployed there too, and even higher seats aren't freed from the obligation either. Shinigami are Shinigami first and foremost. A division's specialization does not immunize its members, rather it takes on more work of that kind than others but only when necessary. The Ninth, for example, doesn't just sit in Seireitei and twiddle their thumbs all day just because Seireitei isn't being invaded. In situations like the present I think it's probably even safe to say that many divisions are on Earth far more often than they are used to.
Divisions other than e.g. the Eleventh and Thirteenth absolutely maintain presences on Earth, just that these two divisions probably have "larger" presences. Just because other divisions have specialities doesn't mean to imply they avoid the duty that defines all Shinigami altogether; rather the higher up on the food chain you are the rarer it is you "cycle out on deployment to Earth" so to speak.
The lower your rank, the "further away" from the division's duty you get and the more you become interchangeable with other divisions—remember past a certain point there can be multiples of the same seat so it's not like there are only 20 officers in every division including the captain and lieutenant.
If you're an unseated Shinigami in e.g. the Sixth odds are you work in the capacity as an MP from time to time in the same way that if you are in the First you perform clerical administrative duties once in a while but for the most part you are still just a Shinigami and you still get sent to Earth. Some divisions are probably a little more unique, such as the Fourth and Twelfth where even lower seated or unseated Shinigami are more "specialized" but the Fourth in particular deploys many of their lower ranks to Earth specifically to serve in that capacity.
So to reiterate: outside the Thirteenth where a presence on Earth is kinda their purpose (and thus all ranks are regularly there), it's common for lower seated Shinigami of all divisions to be deployed there too, and even higher seats aren't freed from the obligation either. Shinigami are Shinigami first and foremost. A division's specialization does not immunize its members, rather it takes on more work of that kind than others but only when necessary. The Ninth, for example, doesn't just sit in Seireitei and twiddle their thumbs all day just because Seireitei isn't being invaded. In situations like the present I think it's probably even safe to say that many divisions are on Earth far more often than they are used to.
