I think it's more of a result from just what people see as the 'ideal role' in said position than the armoury system itself. I played FFXI till midway through CoP and always found that if you weren't a mage job, you'd pretty much spent hours just... waiting. Waiting for xp parties, waiting for BCNM, waiting for anything because 'well that job isn't neccessary so we don't need you'. In the end a job, was like an RL job, if you wanted to get somewhere you pretty much had to network yourself (ie get a linkshell, form statics, etc.) or start lvling whatever was in demand(which was what happened to my Brother and he got to experience the gist of FFXI while I pretty much just gave up and watched him), so nonetheless the same problem was still around back then anyways.

This quickswitch function counteracts that, so one would spend LESS time waiting around for an accepting party, and makes lvling to whatever is in demand a lot quicker. You wanna adapt to survive, not be the same and rot at lvl25 for a good week (which is what happend to me in FFXI).

Also the quickswitch allows those people with only few jobs lvled. I guess i'm lucky, but I've only have two jobs at 50 at the moment. And had parties kind enough (I assume) to switch to another job for me so I can play the role I have, and I'd do so for others as well if I'm able to switch to my secondary job.

I know it's nice to have more job specialization, but I don't want to wait 5 hours for that one job either. And unfortunately people are oppurtunists as well, if all the jobs were to be balanced out, people would still go for whatever job DPSs the highest and what not (even if it was 'balanced' there'd be that miniscule factor that hardcore players would scrutinize about), it happens with any game that gives you a list of choices.