Sadly while this should be the case, it's not currently how it works. It would cause too much fluxtuation and people switching jobs otherwise, and the duty server is already taxed enough as it is.

It does look at the queue and depending on that selects a job that is in need for the reward, however it does this at fixed intervals, and so rarely that it makes the "Adventurer in need" no real guideline as to what job is wanted the most for it. For instance, if you are the first to sign up for something right as it does it's check, it will display needing DPS for the duration of the time while there's no real need for them to speak of.

I'd love it if we were to be given a list where we can see who is currently in the queue (inter-server), and lets you select a party to join.