To certain extent I agree with OP.
I don't particularly like the way jobs are changed on the go depending what the situation requires, but it's sadly what the game is and I have sort of learned to live with it.
I think we will see some change in this however when 2.0 comes out because we will have smaller inventory space, so we won't be able to carry as much gear with us as we have been.

What comes to people changing to jobs they aren't comfortable with... Only a foolish party/event leader forces people on jobs they are not skilled with and if you want to get anything done, I suggest you avoid groups like that. So far 14 favours small groups (I consider 8 man static small) so it hasn't been TOO difficult to put together a group and find the strengts and weaknesses of everyone. I think this job issue really is for pick up groups and well... pick up groups are a bit hit and miss no matter what.

I have picked 3 jobs that I will play and if that's not good enough then gtfo and let me find people who are happy with it. I will make sure that the ls or the static knows that these 3 jobs are the only ones I play and even if I level another job on my spare time, I will only attend events on one of the 3 jobs I have geared up and have experience with.

I think it really was like that in 11 as well, eventhough you had to go to Moghouse to switch jobs. I have MANY times warped back from sea or w.e and changed to another job because for some reason the setup wasn't working.